I want to laugh at though who are saying, they wouldn't hang anything on drywall not even a picture and then point out that it may not have studs.
That's pure BS. First things first. Build codes require studs in all walls, load bearing or not, they could be metal studs vs wood studs, they are just as good at carrying a load. That said, it could be hanging off of sound isolation brackets that allow for small movement, but they're still secure.
Also for apparent dwellings with fire ratings, even in the least coded area's are going to require 1/2" drywall for fire seperation.
On to the next thing. As long as you're hanging it on the vertical surface and not out of the ceiling, and you have appropriately weighted toggle bolts/drwall isolating screws, it can hold a really heavy load. I've got art work and mirrors weighing > 50lbs and have never had a problem. Note that I wouldn't hang 50lbs from the ceiling w/ a toggle bolt as it will pull through, but hanging it on a wall, the stress is mostly in compression as apposed to in tension (i.e. the stress is mostly trying to push the bolt down through the drywall compressing the material below it, while in the ceiling it doesn't have material below it, so it the strength to punch a hole through it.)
With 15lbs I wouldn't even buy a specialty bolt, 4 screws w/ plastic drywall anchors will do. My rear speakers are mounted on a vertical wally for the past 5yrs this way, and they weigh in at 14lbs each. Note at my old house when the were in the ceiling (same speakers) I put a 2x4 wood cross member above the drywall and screw the brackets through the drywall into the cross member.
Samsung PN64D550 (Home Theater Setup)
Denon AVR-3808CI - Mirage FRx Speakers
Samsung UN50H6350 (Living Room)
Yamaha HTR6130 - Polk RTi/CSi Speakers
Samsung UN32EH5000 (Master)