Don’t send it to me - I’m unlikely to be able to open it at all on a five year old iMac.
See if you can open it yourself, and at least try Purge - do that via Model Info/Statistics/Purge unused.
If you saved the file with either or both of Outliner or Component browser windows open, it will take even longer to open.
You could try opening a new file, setting those windows either minimised or better, closed, then try Importing your backup renamed .skp file. And THEN try Purge unused via Model info - it would take an AGE for the Component browser window to open and fill.
Steve Baumgartner (@slbaumgartner) has an extension called Entity Counts which will check a model for the ‘heaviest’ components in terms of edges and faces. It’s now in either Extension Warehouse or SketchUcation plugin store - sorry, I can’t remember which. Probably the latter.
Just seen your upload.
Does it give the Unexpected File format message, or just take forever to open? Wait, if it’s the latter.
And no file history copy, or earlier saved or backed up version?