I have used Rhino 5 for a long time on my mac with no problem before, but now that I have Rhino 8 everything is taking a very long time. I have so far only been working with simple wireframe drawings in top view in Rhino 8, so I see no reason for the program to be this slow.
Hi Karsten, I have checked the file you sent.
I am not sure if you have imported this file or exploded all the geometry but instead of hatches (brick walls) and blocks (plants, trees, etc.), they are just curves.
For example, this tree has 1343 curves:
If you can change them in blocks, file size and performance should improve drastically: Using Blocks [McNeel Wiki]
it’s not just a matter of creating different blocks with each group, but of replacing them, so that you have one block of a plant, for example, and several instances of that block.