The long loading times were mainly caused by how we are (were soon) loading proxies/proxy materials into the scene. So in case you do experience this at the moment and are using the latest versions, you could temporarily import the files directly into SketchUp. I understand if that isn't feasible though with your project(s).
Great to hear that you have pin pointed the issues Good work! is the bug fixed in the latest preview (3.5.8), or is it still under developement?