diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index e89f95a8d..909fbeb66 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -186,9 +186,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          # Most popular Ubuntu LTS version
-          - name: Ubuntu 24.04
-            container: ubuntu:24.04
+          # Oldest supported Ubuntu LTS version
+          - name: Ubuntu 22.04
+            container: ubuntu:22.04
     container:
       image: ${{ matrix.container }}
       env:
@@ -234,9 +234,9 @@ jobs:
     strategy:
       matrix:
         include:
-          # Oldest supported Ubuntu LTS version
-          - name: Ubuntu 22.04
-            container: ubuntu:22.04
+          # Most popular Ubuntu LTS version
+          - name: Ubuntu 24.04
+            container: ubuntu:24.04
     container:
       image: ${{ matrix.container }}
       env:
@@ -256,7 +256,7 @@ jobs:
       - name: install pip
         run: apt install -y python3-pip
       - name: install Python dependencies
-        run: pip install requests psutil monotonic zmq deepdiff
+        run: python3 -m pip install --break-system-packages requests psutil monotonic zmq deepdiff
       - name: configure git
         run: git config --global --add safe.directory '*'
       - uses: actions/checkout@v5
@@ -272,15 +272,26 @@ jobs:
       - name: create dummy disk drives for testing
         run: tests/create_test_disks.sh >> $GITHUB_ENV
       - uses: ./.github/actions/set-make-job-count
-      - name: tests
+      - name: build
         env:
-          CTEST_OUTPUT_ON_FAILURE: ON
-          DNS_PUBLIC: tcp://9.9.9.9
           CMAKE_BUILD_PARALLEL_LEVEL: ${{env.MAKE_JOB_COUNT}}
         run: |
           ${{env.CCACHE_SETTINGS}}
           ${{env.BUILD_DEFAULT}}
-          cmake --build build --target test
+      - name: run tests except core_tests
+        env:
+          DNS_PUBLIC: tcp://9.9.9.9
+        run: ctest --test-dir build --output-on-failure -E core_tests
+      - name: use reduced slow-hash iterations for core_tests
+        if: github.event_name == 'pull_request'
+        env:
+          CFLAGS: -DMONERO_CRYPTO_SLOW_HASH_ITER=20
+          CMAKE_BUILD_PARALLEL_LEVEL: ${{env.MAKE_JOB_COUNT}}
+        run: |
+          cmake -S . -B build --fresh -D ARCH="default" -D BUILD_TESTS=ON
+          cmake --build build --target core_tests
+      - name: run core_tests
+        run: ctest --test-dir build --output-on-failure -R core_tests
       - name: save ccache
         uses: actions/cache/save@v5
         if: github.event_name != 'pull_request' && steps.ccache-restore.outputs.cache-hit != 'true'
diff --git a/src/crypto/slow-hash.c b/src/crypto/slow-hash.c
index 47ae2dab8..be3ad2425 100644
--- a/src/crypto/slow-hash.c
+++ b/src/crypto/slow-hash.c
@@ -44,8 +44,12 @@
 
 #include <errno.h>
 
+#ifndef MONERO_CRYPTO_SLOW_HASH_ITER
+#define MONERO_CRYPTO_SLOW_HASH_ITER (1 << 20)
+#endif
+
 #define MEMORY         (1 << 21) // 2MB scratchpad
-#define ITER           (1 << 20)
+#define ITER           MONERO_CRYPTO_SLOW_HASH_ITER
 #define AES_BLOCK_SIZE  16
 #define AES_KEY_SIZE    32
 #define INIT_SIZE_BLK   8