easy to test, paint a large swath of grass use say a 100m wide brush do a couple of strokes and watch the stats performance tank. you should find your hundreds of FPS drop to 10’s quickly. the problem being that the vegetation is not even visible in the viewport and it tanks the performance even when it’s offscreen. I wonder if while it’s not being rendered it’s also actually rendering it or spending cycles thinking about it instead of culling it. additionally you can see this behaviour if you dont tank your FPS too much but getting close to the grass so you can test the near/far settings which will have no effect on FPS.