Due to the complexity of performance testing in Mendix by simulating the xas requests, it could be better to just not do it.
I think you're bettor off by trying to use free tools for monitoring performance like the nanoprofiler.
https://marketplace.mendix.com/link/component/118285
You could also check slow running queries by looking into the logs of you application for the following messages
WARNING - ConnectionBus_Queries: Query executed inWARNING - ConnectionBus_Queries: Query executed in ...
This will let you know which SQL queries took how much to execute.
Hope this helps!