diff --git a/scylla-cql/src/frame/response/cql_to_rust.rs b/scylla-cql/src/frame/response/cql_to_rust.rs
index a2a450ea9..89330c6e4 100644
--- a/scylla-cql/src/frame/response/cql_to_rust.rs
+++ b/scylla-cql/src/frame/response/cql_to_rust.rs
@@ -10,6 +10,11 @@ use std::net::IpAddr;
 use thiserror::Error;
 use uuid::Uuid;
 
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
+#[allow(deprecated)]
 #[derive(Error, Debug, Clone, PartialEq, Eq)]
 pub enum FromRowError {
     #[error("{err} in the column with index {column}")]
@@ -29,6 +34,10 @@ pub trait FromCqlVal<T>: Sized {
     fn from_cql(cql_val: T) -> Result<Self, FromCqlValError>;
 }
 
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
 #[derive(Error, Debug, Clone, PartialEq, Eq)]
 pub enum FromCqlValError {
     #[error("Bad CQL type")]
@@ -99,6 +108,10 @@ impl<T: FromCqlVal<CqlValue>> FromCqlVal<Option<CqlValue>> for Option<T> {
 ///
 /// impl_from_cql_value_from_method!(MyBytes, into_my_bytes);
 /// ```
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
 #[macro_export]
 macro_rules! impl_from_cql_value_from_method {
     ($T:ty, $convert_func:ident) => {
diff --git a/scylla/src/transport/errors.rs b/scylla/src/transport/errors.rs
index 778f33f29..668fa94df 100644
--- a/scylla/src/transport/errors.rs
+++ b/scylla/src/transport/errors.rs
@@ -34,15 +34,15 @@ use thiserror::Error;
 
 use crate::{authentication::AuthError, frame::response};
 
-use super::{
-    iterator::NextRowError,
-    legacy_query_result::IntoLegacyQueryResultError,
-    query_result::{IntoRowsResultError, SingleRowError},
-};
+use super::iterator::NextRowError;
+#[allow(deprecated)]
+use super::legacy_query_result::IntoLegacyQueryResultError;
+use super::query_result::{IntoRowsResultError, SingleRowError};
 
 /// Error that occurred during query execution
 #[derive(Error, Debug, Clone)]
 #[non_exhaustive]
+#[allow(deprecated)]
 pub enum QueryError {
     /// Database sent a response containing some error with a message
     #[error("Database returned an error: {0}, Error message: {1}")]
@@ -115,6 +115,11 @@ pub enum QueryError {
 
     /// Failed to convert [`QueryResult`][crate::transport::query_result::QueryResult]
     /// into [`LegacyQueryResult`][crate::transport::legacy_query_result::LegacyQueryResult].
+    #[deprecated(
+        since = "0.15.1",
+        note = "Legacy deserialization API is inefficient and is going to be removed soon"
+    )]
+    #[allow(deprecated)]
     #[error("Failed to convert `QueryResult` into `LegacyQueryResult`: {0}")]
     IntoLegacyQueryResultError(#[from] IntoLegacyQueryResultError),
 }
@@ -181,6 +186,7 @@ impl From<QueryError> for NewSessionError {
             QueryError::BrokenConnection(e) => NewSessionError::BrokenConnection(e),
             QueryError::UnableToAllocStreamId => NewSessionError::UnableToAllocStreamId,
             QueryError::RequestTimeout(msg) => NewSessionError::RequestTimeout(msg),
+            #[allow(deprecated)]
             QueryError::IntoLegacyQueryResultError(e) => {
                 NewSessionError::IntoLegacyQueryResultError(e)
             }
@@ -204,6 +210,7 @@ impl From<response::Error> for QueryError {
 /// Error that occurred during session creation
 #[derive(Error, Debug, Clone)]
 #[non_exhaustive]
+#[allow(deprecated)]
 pub enum NewSessionError {
     /// Failed to resolve hostname passed in Session creation
     #[error("Couldn't resolve any hostname: {0:?}")]
@@ -286,6 +293,11 @@ pub enum NewSessionError {
 
     /// Failed to convert [`QueryResult`][crate::transport::query_result::QueryResult]
     /// into [`LegacyQueryResult`][crate::transport::legacy_query_result::LegacyQueryResult].
+    #[deprecated(
+        since = "0.15.1",
+        note = "Legacy deserialization API is inefficient and is going to be removed soon"
+    )]
+    #[allow(deprecated)]
     #[error("Failed to convert `QueryResult` into `LegacyQueryResult`: {0}")]
     IntoLegacyQueryResultError(#[from] IntoLegacyQueryResultError),
 }
diff --git a/scylla/src/transport/iterator.rs b/scylla/src/transport/iterator.rs
index 8d7c07be3..f11d9dd73 100644
--- a/scylla/src/transport/iterator.rs
+++ b/scylla/src/transport/iterator.rs
@@ -1154,6 +1154,10 @@ mod legacy {
     }
 
     /// Couldn't get next typed row from the iterator
+    #[deprecated(
+        since = "0.15.1",
+        note = "Legacy deserialization API is inefficient and is going to be removed soon"
+    )]
     #[derive(Error, Debug, Clone)]
     pub enum LegacyNextRowError {
         /// Query to fetch next page has failed
diff --git a/scylla/src/transport/legacy_query_result.rs b/scylla/src/transport/legacy_query_result.rs
index 599174320..91fe47a58 100644
--- a/scylla/src/transport/legacy_query_result.rs
+++ b/scylla/src/transport/legacy_query_result.rs
@@ -11,6 +11,11 @@ use uuid::Uuid;
 
 /// Trait used to implement `Vec<result::Row>::into_typed<RowT>`
 // This is the only way to add custom method to Vec
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
+#[allow(deprecated)]
 pub trait IntoTypedRows {
     fn into_typed<RowT: FromRow>(self) -> TypedRowIter<RowT>;
 }
@@ -28,6 +33,10 @@ impl IntoTypedRows for Vec<result::Row> {
 
 /// Iterator over rows parsed as the given type\
 /// Returned by `rows.into_typed::<(...)>()`
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
 pub struct TypedRowIter<RowT: FromRow> {
     row_iter: std::vec::IntoIter<result::Row>,
     phantom_data: std::marker::PhantomData<RowT>,
@@ -185,6 +194,10 @@ impl LegacyQueryResult {
 
 /// An error that occurred during [`QueryResult`](crate::transport::query_result::QueryResult)
 /// to [`LegacyQueryResult`] conversion.
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
 #[non_exhaustive]
 #[derive(Error, Clone, Debug)]
 pub enum IntoLegacyQueryResultError {
@@ -205,6 +218,11 @@ pub enum IntoLegacyQueryResultError {
 /// Expected `LegacyQueryResult.rows` to be `Some`, but it was `None`.\
 /// `LegacyQueryResult.rows` is `Some` for queries that can return rows (e.g `SELECT`).\
 /// It is `None` for queries that can't return rows (e.g `INSERT`).
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
+#[allow(deprecated)]
 #[derive(Debug, Clone, Error, PartialEq, Eq)]
 #[error(
     "LegacyQueryResult::rows() or similar function called on a bad LegacyQueryResult.
@@ -259,6 +277,11 @@ pub enum FirstRowTypedError {
     FromRowError(#[from] FromRowError),
 }
 
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
+#[allow(deprecated)]
 #[derive(Debug, Clone, Error, PartialEq, Eq)]
 pub enum MaybeFirstRowTypedError {
     /// [`LegacyQueryResult::maybe_first_row_typed()`](LegacyQueryResult::maybe_first_row_typed) called on a bad LegacyQueryResult.\
@@ -273,6 +296,11 @@ pub enum MaybeFirstRowTypedError {
     FromRowError(#[from] FromRowError),
 }
 
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
+#[allow(deprecated)]
 #[derive(Debug, Clone, Error, PartialEq, Eq)]
 pub enum SingleRowError {
     /// [`LegacyQueryResult::single_row()`](LegacyQueryResult::single_row) called on a bad LegacyQueryResult.\
@@ -287,6 +315,11 @@ pub enum SingleRowError {
     BadNumberOfRows(usize),
 }
 
+#[deprecated(
+    since = "0.15.1",
+    note = "Legacy deserialization API is inefficient and is going to be removed soon"
+)]
+#[allow(deprecated)]
 #[derive(Debug, Clone, Error, PartialEq, Eq)]
 pub enum SingleRowTypedError {
     /// [`LegacyQueryResult::single_row_typed()`](LegacyQueryResult::single_row_typed) called on a bad LegacyQueryResult.\
diff --git a/scylla/src/transport/load_balancing/default.rs b/scylla/src/transport/load_balancing/default.rs
index 89220fbf2..16fd6ac9a 100644
--- a/scylla/src/transport/load_balancing/default.rs
+++ b/scylla/src/transport/load_balancing/default.rs
@@ -2853,6 +2853,7 @@ mod latency_awareness {
                 | QueryError::DbError(DbError::RateLimitReached { .. }, _) => false,
 
                 // "slow" errors, i.e. ones that are returned after considerable time of query being run
+                #[allow(deprecated)]
                 QueryError::DbError(_, _)
                 | QueryError::CqlResultParseError(_)
                 | QueryError::CqlErrorParseError(_)
diff --git a/scylla/src/transport/session.rs b/scylla/src/transport/session.rs
index 11b413dad..90bdfead4 100644
--- a/scylla/src/transport/session.rs
+++ b/scylla/src/transport/session.rs
@@ -83,6 +83,7 @@ pub use crate::transport::connection_pool::PoolSize;
 
 // This re-export is to preserve backward compatibility.
 // Those items are no longer here not to clutter session.rs with legacy things.
+#[allow(deprecated)]
 pub use crate::transport::legacy_query_result::{IntoTypedRows, TypedRowIter};
 
 use crate::authentication::AuthenticatorProvider;
diff --git a/scylla/src/transport/speculative_execution.rs b/scylla/src/transport/speculative_execution.rs
index 60344d0a0..756ed3d89 100644
--- a/scylla/src/transport/speculative_execution.rs
+++ b/scylla/src/transport/speculative_execution.rs
@@ -110,6 +110,7 @@ fn can_be_ignored<ResT>(result: &Result<ResT, QueryError>) -> bool {
             QueryError::EmptyPlan => false,
 
             // Errors that should not appear here, thus should not be ignored
+            #[allow(deprecated)]
             QueryError::NextRowError(_)
             | QueryError::IntoLegacyQueryResultError(_)
             | QueryError::TimeoutError