So, I go over to the local lanes to get in a couple games of practice during lunch. The lanes are oiled around 4pm for leagues and are basically toast by the time I get there at noon. After trying to find the pocket for the entire first game with sporadic results, I decided to roll my spare ball for the second. They have ball speed indicators on the display and I noticed I was throwing my 16lb White Dot (circa 1977 edition) around 15 mph. I thought this was odd as I throw my 15lb Impulse around 14 mph. One would think a lighter ball would go slightly faster. So I jotted down some numbers and averaged about .2 mph faster with the heavier ball. I suppose it could be attributed to gravity during the back-swing or maybe I'm a little smoother with the heavier ball. So now I'm questioning my decision to drop down to 15lbs. I know for a fact that the old White Dot hits a ton harder. Comments?

In a word...friction

Normally, one's spare ball is the same weight as your strike ball or 1 lb. lighter. I think it is very unusual to have a spare ball 1 lb. heavier than your strike balls.

I'd suggest that you try a 15 lb. spare/polyester ball. I'd also believe that it would be about 2 mph faster than your 15 lb. strike ball, not just your 1 mph that you see with your 16  lb. one.

Also the friction from side roll slows the ball as it makes a turn

Charlest:
I agree it is unusual for the spare ball to be heavier. It's a leftover from 1977 that I still had when I got back into bowling earlier this year. My primary ball is a hybrid reactive Impulse. I kept the old ball for spares until I find something new. The old white dot, although heavier, is dead set predictable every time. I can count on it moving 4-5 boards every time in all conditions. Makes it a little hard to part with after seeing all the new plastics that seem inferior to the old stuff. YMMV.