I can only speak from my personal experience here and I’ll be honest this sounds fairly normal.
However it depends on how big a file you are talking about here.
A 1GB file for myself can take 30-60 seconds to open and my 2GB files can take almost 10 minutes (I work with models with up to 1000+ parts on fairly frequently)
You may be able to decrease your times (and maybe file sizes) by making sure that any surfaces that should or can be, are joined; e.g. exploded cube of 6 separate surfaces vs closed cube 1 poly-surface.
I’ve worked with so models given to myself in blocks and when I explode the block I have hundreds of un-joined surfaces that should be 1 poly-surface.