just an FYI.
I also posted this question on the answerhub, and people there were advised against using static lighting for foliage and big scenes like mine.
I played around with the shadow distance and grass distance. In a packaged build I got 45-70FPS in 1920x1080 on epic settings ofcourse.
So i’m happy with the performance results now. No static lighting, only cascaded shadows and distance field shadows.
The distance field shadows help out A LOT!