I absolutely agree with @D3Pixel. That's definitly something worth beeing reported and shown to public as a glimse of what VR can become in the future. This already is a very inspiring project that you are on my friend and I'm sure it will inspire others, no matter how far you have gotten by now.
I still don't see playing instruments in VR at least on the point that we are now. That may change when we have handtracking solutions up and running for everyone. I also think that asio compability will take some time.. the vr apps/instruments that i used had ugly lactency.
Did not measure it but since I claim to have a well rhythmic perception my guess is 60ms at least.
I got that you sorta moddeld a user interface that can be used in VR in order to trigger already existing VST instruments that run via asio in your daw?
But Orf instruments may already work without asio for therapeutic purposes since latency won't be that important. Forgot his name, but there is a guy around this forum with a very medical approach to VR, he might for sure get to know more about this topic for sure.