Actually, the truth is if I have grass instances in my level and the whole tri-count added to the scene with “grasses only” is like 100k tris, I get a lot of frame drops. But If I remove all the grasses and add a single mesh (like a car) that is for example 500k tris, I don’t have any fps drops. So tri-count and LODs aren’t really the issue. I just think there’s something wrong with the foliage tool or something.
Also like fanzypantz mentioned, when hiding the foliage its not being rendered so all the frames should be back when the engine isn’t rendering a single grass out of the many that are placed. But in fact even though it’s not rendering them it’s still using a lot of frames for it and as soon as we delete the hidden foliage from the level frames are back up.
I used to have a LOT of foliage in my levels in cryengine without any fps drop with same PC. Never cared for tri- count and LODs and spent more time detailing my grasses and everything but ever since I switched engines I’m keeping my grasses as cards, no wind volumes, no touch bending, etc. yet, a lot of performance taken for it.