Thanks for playing, and glad you like it! Sorry to hear though you got stuck at the beginning.
The colliders need a bit more optimization. Other than that, the zombies pick up speed when you are in their range since they sense you. Ideally wait till they are out of view, and you will be able to move past them. Yes, they also move at the same frame rate as everything else, with that said, I don't have the player or zombies delta timed, so it could be the game runs a bit faster on your machine.
I'll let you know when I drop the next update!