Bob, since I normally agree with most of what you post, please explain your statement. For a right hander, leaving 9 pins usually is a result of entry angle to the pocket. I hinted to the fact that the carry problem could be due to the ball being in the wrong phase when it gets to the pocket, but most of what I see on house shots have more to do with the ball coming in high and hooking past the 9 pin.
I have also seen what looked like solid pocket hits leave I pins. On a lot of 8 pin leaves, the player is playing deeper and the ball rolls out and deflects away from the 8 pin after hitting the pocket and drops off the pin deck going more through the 9 pin instead of splitting the 8/9.
7 pin leaves are often caused again, by entry angle. In this case, the angle being too sharp, coming in behind the head pin and pushing pins in front of the 7. Again, these often seem like solid pocket hits.
My point above was that 15 mph ball speed is not likely the problem regarding carry. No way to tell the culprit unless we see him bowling.