Reducing your speed by holding your ball lower only works if you have a free armswing, otherwise you will pull the ball into the back swing and muscle it down from there and still have the same speed you had at the start.
There are several solutions to slowing your ball speed:
1. Throw a ball with more surface, the rougher surface on a ball, the more it grabs the lane and slows down.
2. Think slow, shorten your approach, take smaller and slower steps, hold the ball lower and let it swing without forcing it.
3. Unload your release. If you go from a cupped wrist to a flat wrist at the release it will cause the ball to grab the lane sooner by producing heavier roll.
These are just a few of the ways to reduce speed, others may chime in with more.
Number 2 will require much training to master and probably some coaching maybe required as well.
Jim