If you're sticking to off road you may want to look at the Badlands, they hook up like crazy but will wear pretty fast on concrete. If you still have the .15 I think you would be able to run the Badlands without loosing too much "umph", if you go with any others look at 2.2" wheels and tires. Trenchers and Dirt Hawgs are great all around tires, I had the Dirt Hawgs in 2.2 and I have the Trenchers in 2.8 and they are both awesome, if you get them in 2.8 you may have to change some gearing. For the body look at J Concepts and Proline.
Yes it is, traxxas has some 2.2 wheels that will fit. I've also run HPI, you just have to make sure the front have bearings and the rear have 12mm hexes. If I were you I'd put the front axles from an electric Rustler on, this would allow you to run hexes all the way around giving you more wheel options as well as allowing you to rotate tires as they wear down.
Trenchers are the best all around tire that I've run, the Dirt Hawgs are second. The dirt Hawgs seemed to wear a little fast for me, at the time most of my runs were on concrete, the 2.2 Dirt Hawgs seemed pretty soft and I haven't run the 2.8 version. I've never run beadlocks but I've read about them adding a good bit of weight, you add that to the added weight of 2.8" off road tires and your .15 may be struggling to turn them. The added weight could be countered by changing the gearing but that can only do so much before the top end is affected and it may cause you to not enjoy your car as much. If you're sticking to at least most of you're driving on dirt, just grab a set of 2.2 Dirt Hawgs. After you're engine either dies or you decide to go bigger look into the 2.8 Trenchers or Dirt Hawgs.
Ha, I just looked at the specs and the 2.8 Dirt Hawgs are actually slightly shorter and narrower than the 2.2 version. The Trenchers are the larger of the three, the following is from the Proline site.