The OpenJ9 infrastructure is somewhat different [for the better] than what I'm used to using internally, but I have only ever seen the shared class cache enabled when the -Xshareclasses [1] option is passed to the JVM. Do these numbers change significantly (especially after a warm-up run) if you add that option to J9's option set?

[1] https://www.ibm.com/support/knowledgecenter/en/SSYKE2_8.0.0/...