The following test fails in the JDK15 CI in non-ZGC configs:

runtime/FieldLayout/OldLayoutCheck.java#id0

Here's a snippet from the log file:

#section:main
----------messages:(5/405)----------
command: main -XX:+UseCompressedClassPointers -XX:-UseEmptySlotsInSupers OldLayoutCheck
reason: User specified action: run main/othervm -XX:+UseCompressedClassPointers -XX:-UseEmptySlotsInSupers OldLayoutCheck
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules java.base,java.management --add-exports java.base/jdk.internal.misc=ALL-UNNAMED
elapsed time (seconds): 25.831
----------configuration:(4/111)----------
Boot Layer
  add modules: java.base java.management
  add exports: java.base/jdk.internal.misc ALL-UNNAMED

----------System.out:(0/0)----------
----------System.err:(16/1077)----------
Java HotSpot(TM) 64-Bit Server VM warning: UseCompressedClassPointers requires UseCompressedOops
java.lang.RuntimeException: Misplaced int field: expected 24 to equal 12
at jdk.test.lib.Asserts.fail(Asserts.java:594)
at jdk.test.lib.Asserts.assertEquals(Asserts.java:205)
at OldLayoutCheck.main(OldLayoutCheck.java:65)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
at java.base/java.lang.Thread.run(Thread.java:832)

JavaTest Message: Test threw exception: java.lang.RuntimeException: Misplaced int field: expected 24 to equal 12
JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.lang.RuntimeException: Misplaced int field: expected 24 to equal 12
----------rerun:(46/6439)*----------

The log file shows that the fix for JDK-8239503 is in place:

requires=vm.bits \=\= "64" & vm.gc \!\= "Z"

but the test is also failing in non-ZGC configs.