17mph is not that slow. Now, the question is, how are you measuring your ball speed? The CATS system, etc. usually used to measure ball speed on the PBA TV shows measures speed closer to the front of the lane. The Qubica scoring system measures ball speed just before the pin deck. Extra time on the lane, friction, and more angle on the backend of the lane than the front part of the lane all combine to make your ball speed lower according to Qubica than CATS for example.