I am not sure why do you need to simplify your visopt, even if Rhino is not out of memory yet…
But never mid. I suppose You use Irradiance map (default option) to calculate the scene, so here is the way how to simplify that>
Min Rate @ -3 Max Rate @ -2
HSph. Subdivs @ 50 Samples @ 20
By default, Max Rate is at 0.
If Your Rhino crashes anyway, try to mesh all objects in the scene.
For even faster scene with lower quality (I don’t recommend that) try:
Min Rate @ -5 Max Rate @ -4
HSph. Subdivs @ 30 Samples @ 15
but this time it’s going to be very very fast, but in my opinion - not good enough even to show it to the client.