Michigunner,
Your math is correct, but a little misleading.
A 15dBA difference in sound intensity does require 2
5 (32 times) increase in sound power. That doesn't mean, however, that the the sound is 32 times as loud.
I found a really good website,
http://www.phys.unsw.edu.au/~jw/dB.html that explains how the dB scale works.
Best of all, there are three sound tracks which you can listen to. The first one shows a broadband sound (I think a gunshot is single frequency..) decreasing by 3 dB at a time. So count off five bands, then click the demo. As you can hear, there is a noticeable difference between the largest bar and the 5th bar. Try the other soundtracks, which are spaced closer together. Much harder to pick out the individual steps.
Bottom Line: 10 or 15 dBA represents a large increase. Continued exposure to anything in the range of a handgun's sound intensity will damage your hearing. (Take a look at road tests in Road & Track magazine, for instance. If there's less than 3 DBA difference between two modes, an average observer won't be able to tell the difference. For instance, I'm looking at a road test of the 2006 Pontiac C6 GTP. Interior noise was measured as 66 dBA at 50 mph, and 70 dBA at 70 mph. From personal experience you know it's a rare car that's not noisier at 70 than 50 mph, so the theory makes sense.)