Use node 15 only

This will speed up CI
In the case where a run does fail, there is less to retry etc
Dockerfile currently uses 15, so just use that...

.github/workflows/netlify-preview.yml

@@ -14,10 +14,10 @@ jobs:
       with:
         env-file: .env.development.mock
 
-    - name: Use Node.js 14.x
+    - name: Use Node.js 15.x
       uses: actions/[email protected]
       with:
-        node-version: 14.x
+        node-version: 15.x
     - run: npm ci
     - run: npm run build
 
@@ -48,10 +48,10 @@ jobs:
       with:
         env-file: .env.development.prod
 
-    - name: Use Node.js 14.x
+    - name: Use Node.js 15.x
       uses: actions/[email protected]
       with:
-        node-version: 14.x
+        node-version: 15.x
     - run: npm ci
     - run: npm run build
 

.github/workflows/node.js.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12, 14, 15]
+        node-version: [15]
 
     steps:
     - uses: actions/[email protected]

package.json

@@ -63,7 +63,7 @@
   ],
   "_id": "[email protected]",
   "engines": {
-    "node": ">= 11.0.0",
+    "node": ">= 15.0.0",
     "npm": ">= 6.4.1"
   },
   "gitHooks": {