SGTBilko:
like how you added the fairway shot to it, I have something very similar but at the 30, 60, 90 scale. I tend to very rarely use the 15 scale for anything over 6 feet.
You could easily use the 15-ft meter if you just divide the 30-ft meter values by 2. An 18-ft putt on the 30-ft scale is the same amount of power as a 9-ft putt on the 15-ft scale.
Multiplying the 30-ft values by 2 would also allow you to remove the 60-ft markings on your meter, leaving only the 30-ft and 90-ft markings.
Up to you, though. *shrug*