Hey, can anyone suggest how to deal with the AI slowdown in long missions?
It's just unbearable to play for 3-5 months. The computer takes 10 minutes per turn. What is it doing?
Is there a way to reduce its turn time?

Yes, I've encountered this too. I can suggest that, to somehow reduce the AI's turn time, don't let the computer create a large number of heroes. Of course, if you haven't met them yet, it's difficult to control the number of enemy heroes. But you need to destroy all encountered enemies mercilessly. The computer usually recruits the maximum number of them, and they are the ones that prolong the turn time. It might sound silly, but it helped me. By the end of the game, there should be only one main computer-controlled hero left, and that's when the final battle will take place.