Once you do a check in changes, it creates a snapshot and saves everything in your project online.
Even if your PC dies, you will be able to restore the snapshot and get your entire map back to how it was when you made the snapshot.
I have made about 240+ snapshots on my current project, checking in at least once a day.
The landscape rebuild should be fine and won’t change any landscape detailing, I think it just recalculates the collision mesh or something, but if you make the online backup, you’ll be safe.
The Project size looks OK, everythings under…
Lets sort your memory calculation out and go from there
I assume you have World Streaming enabled, in World Settings what Cell Size and Loading Range are you using ?
When you launch a session move around a bit and see the different memory counts in different areas, move far away from everything until your memory thermometer goes as low as its going to get, how much is it at ?
Find your area of highest memory usage, usually near centre, how much is that ?