Are you sure it wasn't Eragon by Christopher Paolini? It's not 15 years old, but the guy who wrote was 15 when he did.
Synopsis in a nutshell: Eragon is a 15-year-old farmhand living with his uncle and cousin in the rural hamlet of Carvahall, located in the northern part of the empire of Alagaësia. One day while hunting in the woods he stumbles upon a mysterious stone, which turns out to be a dragon's egg. The dragon hatches, and dragon and boy develop a mental bond. With a little help from Brom, the local sage (whom we know will soon become the boy's mentor, closer to Obi-Wan than Gandalf), Eragon names the dragon Saphira, after the first of the Dragon Riders, an ancient class of warriors now thought to be long-extinct.
In no time there's Trouble in River City. Creepy henchmen of the evil emperor Galbatorix come to town searching for the egg and, in Star Wars fashion, Eragon returns home to the farm to find the place razed to the ground and his uncle at death's door. Vowing vengeance upon the killers, Eragon sets off with Saphira and Brom southward, and Brom fills Eragon and us in on the history of the empire, the Dragon Riders, and why Galbatorix is so desperate to get Saphira into his clutches. Eragon and Saphira's bond grows, and soon he is a full-fledged Rider. We also learn that there is, of course, much more to Brom than meets the eye; he's involved with a growing revolt against Galbatorix from a shadowy organization known as the Varden. And there was also a reason Saphira's egg was where it was when Eragon found it. Eragon soon realizes that his Destiny is intertwined with this revolt, and he must reach the Varden — as well as solve the riddle of the dreams he keeps having of an imprisoned elf princess — before he is captured by Galbatorix's ravening hordes of Orcs...er, I mean Urgal.
More info at
http://www.sfreviews.net/eragon.html