From my profiling, the checksum calculation isn’t excessively expensive, the majority of time is spent in the actual database interaction. If you are seeing Class.getGenericInterfaces as the most expensive portion it sounds like the checksum calculation isn’t the expensive part either.
I saw some performance issues with tests running on Linux in the reflection code, but that was resolved by changing the mock object usage. You may be running into something similar, we do use a lot of reflection at times.
Could you send me the profiling information you are getting? If you would prefer, you can email it to me at firstname.lastname@example.org