Lumen is enabled by default in all UE5 projects and it’s not supported in VR as of now - that’s primarily why you’re seeing poor performance.
The new VR Template in UE5 and 4.27 has been tested for the Reverb G2. In UE5 disable Lumen in Project Settings (search for “Global Illumination”) by setting it to “None”. This is temporary and will be fixed when UE5 is no longer in Early Access. As long as the Reverb G2 is connected and working you can now click the VR Preview button to play the VR Template in VR!