First, because it's really not clear, as a newcomer, that tests in integrationtest/performance are ORM performance tests, or even that tests in integrationtest/sandbox are actually performance tests too...

Second, because I'm going to add elasticsearch performance tests and currently I don't know where to put them to keep things tidy.

I think having a intermediary directory integrationtest/performance where we have "engine", "orm" and "sandbox" subdirectories should make things clearer.