Our test suite runs 19 minutes on 9.2.9.0 but 87 minutes on 9.2.10.0. No other changes just replacing the ruby gives the slow performance. I tried to play with memory settings but no significant difference.
We are running on jdk 11. I've noticed the problem on jruby-head but thought you had left there some debugging.

Environment Information

Provide at least:
java version "11.0.6" 2020-01-14 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.6+8-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.6+8-LTS, mixed mode)

• JRuby version 9.2.9.0/9.2.10.0 and no flags, default JRUBY_OPTS
• Operating system and platform (e.g. uname -a)
  macOS catalina and Ubuntu 16.04
  Other relevant info you may wish to add:
• Installed or activated gems
• Application/framework version rails 5
• Environment variables