That's pretty much what ghouls are about. They walk slowly but once they are close to you, it's pretty much over (Unless you are really overpowered). I did some testing and they work as intended. I waited in a cave for ghoul to spawn at t he oter side of the screen. Once he did, I saved the game, loaded it again and he was still walking because he was not close to me when I did save. Same with using speed potion. He only started sprinting when he was very close.
Fun fact, ghouls have speed 5 when they sprint. Speed potion also gives you speed 5, but because of how enemy movement is handled, you will be slightly faster.