Ah, I thought you were upgrading from the .15 to the .25. My bad. Then those will be a direct swap.
And I would think the engine woudl come with the carb, unless they both use the same carb and they suggest using yoru current carb. Swapping them out is not hard, you just have to make sure to push it down to seal the carb on the block. Before you do, I would take your carb apart and clean it out with carb cleaner just in case there is some trash in teh needles. But, if you really want to know if it coems with the carb, I would call your LHS or Traxxas and ask them.