I feel like it has to be Williams for 3 reasons: 1) No way they would let some other composer write a new theme like that and put it in a Star Wars trailer 1 month before the movie opens. No way. All of the other trailers have contained either old Williams music or music that did not contain thematic material. The theme has to be Williams. 2) Strings starting at 0:19 are a technique that Williams loves to use (not that someone else couldn't copy this) and is also a technique very hard to get right using samples, so it lends to the idea that all of this is recorded by live players, which is what I would bet (except for the drums, which may have been added in) 3) At 0:42 (most audible at 0:45) there seems to be another short statement of a new theme in the horns. Again, no way another composer would be allowed to be putting new themes into trailers at this point. So I'm voting for this is definitely Williams and definitely from the score. All IMO of course. And of course, edited and mixed specially for the trailer.