Yes, my spare ball is 14 while the rest are 15 lbs.
I did it because I am rarely throwing it at more than 1 or 2 pins, so why have the extra wear and tear on muscles, tendons, ligaments, joints, etc? Think of how many times over your lifetime you use a spare ball.
I have never had any issues with timing because of the ball feeling slightly lighter. If your mechanics are the same it shouldn't hurt you. If you change your mechanics to throw it harder, or softer, or whatever, then you may develop an issue.
Muscles don't have memories, but brains do. There are no brain cells in muscle tissue. The muscles can only respond to impulses from the brain.
To each his own though... There is no right or wrong, just what works best for you.