KIE Server client does not reuse marshaller for JMS calls. It does for REST ones.

JMS:
https://github.com/kiegroup/droolsjbpm-integration/blob/eb3eccc059fe0d2e169d6504df23e7aabff38885/kie-server-parent/kie-server-remote/kie-server-client/src/main/java/org/kie/server/client/impl/AbstractKieServicesClientImpl.java#L507

REST:
https://github.com/kiegroup/droolsjbpm-integration/blob/eb3eccc059fe0d2e169d6504df23e7aabff38885/kie-server-parent/kie-server-remote/kie-server-client/src/main/java/org/kie/server/client/impl/AbstractKieServicesClientImpl.java#L83

This dramatically reduces performance when compared to REST.

Performance test results (with fix means with reusing the marshaller):

REST 1 thread / JMS 1 thread with fix / JMS 1 thread without fix
Median duration of one command: 45.3357 ms / 53.9975 ms / 144.3902 ms
Throughput (op/s): 18.7283 / 15.2076 / 6.5735

REST 4 threads / JMS 4 threads with fix / JMS 4 threads without fix
Median duration of one command: 46.9026 ms / 52.2510 ms / 150.9012 ms
Throughput (op/s): 82.5232 / 71.9900 / 20.3512

REST 8 threads / JMS 8 threads with fix / JMS 8 threads without fix
Median duration of one command: 48.5974 ms / 56.5077 ms / 211.4696 ms
Throughput (op/s): 117.1528 / 98.0171 / 31.2132