Few things to keep in mind:
- Outdoor areas are more expensive in general because you can see lots of stuff
- Because of point 1, try to use instances as much as you can, to reduce draw calls, which is the main culprit for low FPS…grass does instancing automatically, but regarding trees, if they’re placed manually, you need to replace them with instances…try to get all their position using Get Actor of All Class, save to an array, feed the array into the transform of the instance
- Usually trees LOD looks very bad in VR, so try to have the LOD switch where is less noticeable
- Check the polycount, because a forest usually has a lot of geometry, so even if 3-4 milion looks fine on desktop, in VR everything is rendered 2 times
- Because of point 4, try using Instance stereo rendering, not sure how many downsides there are for this.
In general, start small, empty terrain with nothing, then add things on top of it and constantly check the polycount and draw calls and see what is your PC limit, basically when your PC drops below 90.