dosfsck: how long does it take to repair a 32GB FAT filesystem on a USB drive?

I have a 32 GB USB stick with totally corrupted filesystem and a laptop with Ubuntu.

I have run the command dosfsck -w -r -l -a -v -t /dev/sdb1 16 days ago and it is still running. It has been using 100% of one cpu all this time.

In stdout I currently see messages like this:

/резюме Enter engineer/Length 8.66>/+φεïτnv.S¥d
  Bad short file name (+φεïτnv.S¥d).
  Auto-renaming it.
  Renamed to FSCK0071.483

which means that it has "repared" 71.5k files? One "auto-renaming" operation takes about 1 minute.

How do you think, is everything OK? Will the process finish successfully? What remaining time estimate could you make?

I am also not 100% sure if the original filesystem was FAT, because the person who gave it to me doesn't even know what a filesystem is. Can you tell in the current situation that it really wasn't FAT and what dosfsck is doing is corrupting it even more?

Finally, what would you suggest the best thing to do in this situation?