I have a large music collection, and whenever MP3Tag starts it sits "reading directory" for a few minutes before I'm able to use the software.
Is it possible to have the software "remember" the file collection from the last time it was run? Maybe it could just scan for changed files rather than scan every song and every tag every time.
Check out Foobar2000 it does a good job of monitoring a large collection.
Funny, my MP3tag remembers the last session ...
perhaps you have to uncheck the Option "Start in this directory".
BTW: 1) let us not compare sizes (of libraries).
2) the impression whether something is slow or not depends very much on the individual planning. I think itunes and Media Player are slow. And MP3tag is much faster. But this only my opinion.