Your DWG file is actually set to units=inches. You think you overcame it my setting UNITS command to meters, which does nothing, that's a major issue that has nothing to do with file size. Hope you know that. It is out of scale, something major is wrong here.
1) Multiple floor plans: there is #1, these two (three) plans ought to be XREFs.
2) There is lots of content in the file, especially around your half-millions square foot floor plan (it's the wrong scale, see comment up top): you also have duplicate objects n the main floor plan: looks like it was copied twice, and not quite perfectly. XREFs usage is not practiced, #2 issue (you like to use blocks for the plans, not as efficient). Your block also contains purgeable content (which as XReFs you could have cleaned up much easier).
3) Multiple other plans and details (and tables) to the sides: issue #3, all need to be xrefs.
Your "green" plan's wall hatches have been exploded. Rookie mistake, #4 issue and may be the primary issue.
What's up with those hundreds of little hatches in little squares everywhere? That's #5 possible issue.
Better workflows and organizing may be your best file. After you fix the scale problem, this file as is remains unusable IMHO.
