Hello,
1. The Mountain works properly, as I tried it the first time you uploaded the xpack.
2. The Stadium needs a lot of work, as the photo textures are not lined up identically on each panel, sketchup will output multiple versions of the same texture all slightly different totaling 360+ images to resize. The track folder will be huge with so many textures for just one building. I'm also concerned that some of the surfaces maybe inside out, but will only know later on.
3. I was waiting for a response before you continued with the walls, as the terrain is defineately the problem and needs deleting. I deleted the terrain and btb exports quickly and the track loads quickly in rFactor aswell.
I'm thinking perhaps to import the terrain from sketchup instead including the mountains to work around the problem.