I've tried to mine the 15 times within 5 minutes -- I've definitely just done it once, and I think more times than that. However, it doesn't get checked off on my quest list.
When I tried to do this quest, I mined, and I mined, and I hit 14, and then I mined some more until my five minutes was up, and it wouldn't budge past 14.
We had some trouble with quests today. Specifically, tasks not being counted toward quest completion, and players not getting proper notification of quest completion. Sometimes a reload triggers the proper notification, sometimes not. We'll dig into this and get things figured out.
Still have this going on. My "Yes, you have no bananas" quest has been done for ages (and multiple reloads) but remains in my list of active quests, even with all the tasks checked off.
Amy Pond: I had to log in as you and remove+re-add the quest, after which I was able to complete it okay. I'm not sure what happened there, but you now have credit. Also, apparently a job finished after you logged off, so I had to click through that dialog to finish the other quest. I don't recall what percentage of the work you did or what your reward was, but it came through okay and you also now have one less quest to worry about. Sorry for all that!
Chelseathing: Did you see if the health bar on your mining pick went down at all or if you lost any energy while mining? Usually there's a message in Local Chat when you try to mine a rock that indicates how much you got from it. Do you remember what that message said, at all?