Is there some kind of non-sanctioned Disney event happening on the weekend of the 15th of December? It seems there's very little resort availablility...
We arrive on the 18th! Lots of schools only have a partial week the week of the 18th, so like us, they pull their kids for the two days before the break begins.
Although Christmas will bring the crowd in, there is a High School Basketball tournament going on that weekend at Disney's Wide World of Sports which probably has a lot to do with the limited availability at the resorts.