If you use the same controller, then unless you change it's settings (if it has a way to do that) it'll put the same power thru the new motor it did thru the old.
If the new motor has the same winding/design etc as the old one (even if it's a different brand/etc, it could), it'll probably run at the same speed.
So what you could do is use the old motor/etc but just install a new controller that has a speed limiter function.
If the new controller you're getting doesn't have a speed limiter function, and the motor it's on is wound/designed the same as the other, it'll probably go the same wheel speed (unloaded) as the first bike. Because of wind resistance, and power needed to go a certain speed, it could end up slower than the first one, but probably not because of the motor itself.
Or just use the throttle judiciously, so it doesn't go too fast.
If for whatever reason you simply can't make yourself use less throttle, and the controller doesn't have a way to do it in settings, you can limit the throttle's max output electrically with some resistors; there's a number of threads discussing how to do that if you need to.