Actually, fully trained by 15 months isn't that unusual. Back 1 generation ago, almost every child was toilet trained by 2 years, reliably, and in the 50's the normal age for complete reliability was 18 months, with many many kids less than that. I was semi-toilet trained at 11 months, but had a regression due to an anal tear on the potty - then took 6 months to get over that. My sister fully TT'd at 17 months. my aunt never had a nappy on after 11 months (and my grandma was quite houseproud!) there are lots of examples. BUT disposables have drastically reduced the incentive for kids to use potty - thus I have recommended to lots of friends to change to cloth at 9 months or so so they start to get the feel. also, there's lots less incentive for parents using sposies!

Apparently starting younger, rather than waiting is the key. (heard recently that a study from scandinavia demonstrated that kids were better off introduced to the potty much earlier than is currently normal. Wish I knew where a copy of that study was.)

as for bargaining with a 10 month old, I guess you woudl tell them every time you put the nappy on, plus let them learn from experience that after a change they are naked. They certainly can learn much before we think they can but I guess it takes lots of repetition - much like for a dog. a dog has the reasoning capacity of roughly a 2 year old, and even a puppy can learn what a 1 year old can learn - pups certainly learn how their actions effect what happens to them very easily. I guess one can only try!