At this point, we really don't know a lot about the calendar in late-November/early-December. Based on the past few years, Candlelight Processional should be happening the first weekend in December. This primarily only impacts DL, but it does tie up Main Street quite a bit. I think there was also a big convention in early December last year that impacted crowds, but I haven't see it on the Anaheim Convention Center calendar for 2015 (yet). There is supposed to be some "new" holiday decor this year, which should be fun to see!
When you say you went the week before Thanksgiving in 2014, do you mean the full week before (i.e., 11/16-22/14) or the week that included Thanksgiving (i.e., 11/23-29/14)? I ask because I went the full week before Thanksgiving and the weekdays were fine, but the weekends did seem to pick-up. There was the Avenger's Marathon (11/13-16/14), but I also felt the crowds really picked up on the following weekend as well (11/21-23/14). I actually think that is pretty common for that time of the year; the weekdays are pretty good, but the weekends are busy. When I've also gone in early-December and the weekdays have been manageable, but the weekends are very busy. It was similar in feel to the full week before Thanksgiving, but with perhaps slightly higher overall crowds.