I think, best I post the general settings of the scene. Should I change something here? I use XP64 and 8GB RAM - maybe I could allow Vray to use more RAM. Could it be done per “Mem Limit”?
It depends on the settings, of course, but for grass, where you need lots of fine details, it can be substantially faster, as it will take less RAM if the map is tiled.
if you have ram to spare, raise the dynamic memory limit, and you’ll avoid the swapping of displaced geometry from ram.
400 megs seem way too low for that kind of detail, to me.