This guide explains how I fixed my issue with lag/stuttering that I encounter at the start of every phasmophobia session.
This guide explains a fix I used for my Oculus Rift, but may work on other headsets as well. It only lasts till the end of the VR-Session, but consistently works.
For me, the lag always occurs in the first game of my Phasmophobia VR-Session. The lag significantly increases when being near objects or while looking around quickly.
After spawning in and experiencing the lag, try to open the virtual desktop in the oculus menu.
Look for the SteamVR box. The one that shows if your headset,controllers etc. are plugged in.
Click on the cross, as if you are going to close it. It will ask you if you are sure.
However, click on cancel.
It does not make sense, but after these steps, it ALWAYS fixes my lag for the remainder of my VR session.