Something I've noticed, after having the game open for roughly two hours (with 3.5k+ guests in the zoo) is that the performance begins to deteriorate, regardless of how low the graphics are dropped to.
Restarting the game fixes it, at least until it repeats, but that's not really an enjoyable thing to have to do.
Restarting the game fixes it, at least until it repeats, but that's not really an enjoyable thing to have to do.