Are you asking about specifically eactly every two weeks, or did you really mean "twice a month" or "every fifteen days which is about two weeks"?

If you just mean making half the payment twice as often - you are saving a little bit in interest. You know what would save you a little bit MORE in interest? Make your ENTIRE monthly payment half a month early. But in the grand scheme - that is not going to shave off ten years. Making an extra payment (especially EARLY in a 30-year mortgage) will have a bigger impact.