Does Back Waxing Hurt
It depends upon a number of factors, one of the most prevalent being the thickness of the hair. I personally find leg waxing to be more painful than back waxing. My back hair is very fine and thin, and comes up easily, and the roots are already small, so it isn't so much painful as weird-feeling (kind of like the face). My leg hair, however, is mostly dark and think with large roots, because I shaved it for 7 years or so, and each time I shaved it grew back thicker. Now that I've started waxing it, the roots are growing back smaller, and each time is less painful than the last, but I am several waxing away from it being painless.
In short, the thicker the hair, the more painful waxing it will probably be.
Another thing to consider is your personal level of pain tolerance, and your level of hydration. If your skin is dehydrated, you follicles will hold onto those roots for all they have. Make sure that before you wax, you drink lots and lots of water, and maybe use some lotion and alcohol-free soaps on the area. You can also take an Advil or ibuprofen before waxing, but avoid numbing cream, because the cleanser they use on the area before applying the wax will take that cream right off.
All in all, if your goal is to have healthier skin, and phase out the thickness and darkness of your leg hair, and have smooth legs for 2+ weeks (instead of 2 days, like you would have with shaving), then the 15 minutes of unpleasantness is definitely worth it.