"Good" performance is always subjective, particularly when evaluated on an emulated platform like RD&T. Having said that, we can say with certainty that any multi-user environment deployed on RD&T that relies on WebSphere or java will probably not perform to your expectations. Any CPU bound workload, (like java,) will experience this behavior on RD&T. There isn't really anything you can do about it, short of deploying on larger, faster, processors. Adding memory doesn't help these cases.
Using WebSphere Liberty helps with startup time. It takes a nominally 5+ minute WAS standalone server startup time down to about 1 minute. Once the server is up, application response time from the Liberty server is about the same as classic WAS.
RDzJohn
RDzJohn