Hi Stefan
For really big models I recommend disabling the automatic quality option (Options-> Automatic quality) before loading the model.
Disabling automatic quality option, a scroll bar appears at the top that allows us to adjust the resolution of the model, avoiding the bar end this avoids having to load the entire model in video memory.
For obj files, the cache system is inefficient and requires parsing the file every time. I recommend using ply or 3ds files, then reload from cache is fast.
Best regards,
Anthony