What was the key to the increase in your ball speed, I recently switched to no thumb and speed has been consistently 14.5mph. Would love to get up to 16.
That's a big question and a bit off topic. Regardless, I'll try to answer it.
There was no one thing I did to change ball speed. There was not tip I learned to get another 3+MPH over night.
A large part of it was just getting more comfortable with my game, and slowly over time using my legs more.
I did try really increasing my back swing a lot for a while - but without my thumb in ball, it just seemed to add too many things that could go wrong. Gradually I realized the more relaxed I was, the more ball speed I had.
Working on slowing everything down helped. It seems paradoxical, but if you try to throw it harder, it just creates muscle tension. I used to be way to fast on the first 2 steps, then not in position for slide. Get more speeding by slowly getting into position, then gently letting it rip for slide and release.
Working out a little, single leg squats for leg strength and then jogging/stretching for flexibility. Helps me use my legs. 3 years ago I was very stiff and it took a whole game at least to warm up so. Now I just need a few shots and can bend down fine without tightness.
Also - this is going to sound really old school, not "modern" and so if people disagree with it, fine. Look at bowlers like Marshal Holeman. Yes, he used his thumb, but a lot similarities to no-thumb bowling. Kept backswing short and simple, and a lot of speed with his legs.
Yeah, if you do that you can't "plant" and get more leverage and thus not "modern." Whatever, my rev rate off release is 420, and I track very high. I need speed and not more leverage.