You running WinOS with only +/-10GB of storage remaining on the C-drive is a problem in whatever scenario you can think of.
First of all, the storage on your C: ain't related to any kind of 'memory usage', so you can't really blame any memory leaks or whatnot.
Only when you 'run out' of available (RAM) memory and you start addressing your page file does it actually matter how much storage you got. At that point, it starts getting slow AF of course, since constantly swapping is a disaster for speed. Your HDD is a gajillion times slower than your RAM after all.
A data drive next to the C: drive that's next to full ain't really an issue, but still ... in any case, you really shouldn't run WinOS on a drive that's nearly full.