well if you're not connected to a network then I guess you are't accidentally installing R packages on a network drive or something like that. That's notoriously slow. But sounds like not your issue.
I agree that 300MB and 220MB are not shockingly big. Mine are a little smaller, but not orders of magnitude:
with procmon I would look for processes that are either 1) sucking up CPU or 2) accessing files on our HD during the time that RStudio is really slow.
Check out this thread. It looks like there might be issues with Windows Defender. Related, are you using Google Drive? That's been known to cause file access contention.