Slowness could cause due to various reasons, and it’s essential to identify if it’s from WebSphere or some other components. To isolate, you can check the following.
Is this slowness for all the users?
Is entire application slow or just particular functionality?
How about accessing JVM URL (bypassing Web server) directly?
If the slowness is found in JVM, then you can take the dump and check the logs to find out the cause. It would be worth checking if there were any release and slowness is just after that.