Rstudio is painfully slow

Just a guess, but ?gctorture says

 Provokes garbage collection on (nearly) every memory allocation.
 Intended to ferret out memory protection bugs.  Also makes R run
 _very_ slowly, unfortunately.

which sounds about right for your problem! You could try

gctorture(FALSE)

If that speeds things up, then look for somewhere that this might have been set, e.g., in a .Rprofile (current working directory, or your user home directory, or the installation directory of R; see ?.Rprofile) and make sure that you start R without loading any .Rhistory or .RData files (again in the working directory, your home directory, etc.)