My guess would be intestinal gas. I worked in an ER for a few years and remember a couple of people coming in for it ... they were a little embarrassed when they found out it wasn't cancer or something horrible, but they were relieved and it went away. Sometimes it hurts without added pressure.
Where it was only a 15 minute bout, that would be my best guess.
>>>I saw your additional comments. Definitely sounds like gas pains ... there is a reason babies cry so much when they have gas - it really hurts. Adults generally get the severe pain less often, but, though it makes me laugh (maybe I'm sophomore-ish), gas can be very painful.
As far as appendicitis, this doesn't sound like the case at all. Wrong abdominal quadrant, not a long enough duration of pain, and appendicitis pain generally is most severe when you release pressure from pushing over the appendix (something I learned while an EMT).
Try just passing it, if you can. If your someplace public or just can't, try Mylanta or some sort of gas medicine. You probably ate something that caused it, and may want to take Mylanta or whatever if you eat that food again.