I think I'm a good tipper. If the service is good I have no problem going over that 15%. I have no problem going below it if its terrible.
Sounds like you go to the same kinda places I do. Of course here in the Bay Area that $13 hair cut is $20 but it's still the cheapest around. $5 is my standard tip as well. That may even too much cause my cut is a #4 on top #3 on the sides. Done in less than 10 minutes.