I never used to offer 15 mins because I thought they'd be guys that wanted 30 mins but were being cheap and would overstay. That would piss me off. But the 15 min ones I get are okay, I charge £20 less than my half hour so still appealing but totally worth it for me. As long as they are quick to cum then I like 15 min bookings, over in a flash really. I do move it along if they are being slow and reiterate it is just a quickie and they are fine with it. Most still choose a half hour but tbh I would be happy with more 15 mins, a better earner per minute!
I do also get the half hour ones that are done in 20 minutes, I like these too!