Hello, I am having this exact same issue but on the VR version of skyrim. I found the EngineFixesVR.ini file but it did not have an experimental tab at all at the bottom, nor any of the values you suggested to change. I added them in at the bottom and saved it, but I'm still experiencing ILS after 30 minutes or more of playing and loading into a new cell. Sorry if this belongs somewhere else, being the VR version and not the SE version, but I have searched everywhere for information on this and this thread is the closest thing I could come to based on what I'm experiencing. I'm not expecting much, but if any of you may happen to know of a similar fix for the VR version for the exact same issue as described, I would forever appreciate you.