FM running incredibly slowly

I'm currently playing a game I started back on 12.1. I'm now playing in 2021 but the game has just become ever so slow, the match day works fine, it's just the processing is horrendous, this was never really the case before. When I started the game it actually ran very fast and I believe I had more league loaded back then than I do now, since I use the add/remove features every now and then to give my career more options.

Is there anything I can do to speed the game up again or reasons it has dropped so dramatically and in a relatively short space of time?

I have stopped having open tabs like I used to when playing but if any difference it is minimal.

I found that when I added a league and then removed it in one of my saves, the actual number of players remains the same. Therefore using the add and remove feature will slow your computer down if you use it a lot. If you look through the preferences stuff you may find some ways of increasing processing times - eg. making the processing fixtures mode "fastest (can't interrupt)".