This is actually caused by the default compatibility setting on the .exe file. I believe it is set to windows 98 compatibility mode. That in itself isn't the problem, the problem is that it forces the game to run on a single CPU core. You can run the game and allow other cores in the task manager, but a simpler solution is simply to remove any compatibility modes (unless that makes the game not run at all, but it works for me on windows 10).
Don't ask me why a game this old cannot run on single core without slowdowns, it's probably something to do with how windows allocates resources, but anyway, if you don't restrict the game, it'll run fine.