In VR, when fps is low the turning speed using the joysticks/trackpads is also slow.
It is thought that a fundamental review of the Input series is necessary.
It is highly likely that the number of times of input judgment is not stable at frame skip.
I need to separate it but I think that futurerequest at new VRChat using Unity 2017 probably helps.
(Naturally, even with a mouse, it is a big problem for AIM that this turn speed becomes unstable during intense shootout)
my guess they programmed that each frame rotates you in some degree just change it over time not frame and your done ?
This is fixed in VRChat 2018.4.3.
VRChat 2018.4.3 is now released, which fixes this issue.