Well, you'd have to do more to make your game with it. C2 has a lot of things already setup for you, whereas kivy leaves that up to you.
Whether or not the end result is faster really depends on you. Python can be slower than JavaScript, but then again it's easier to use c or something for the time critical parts if needed. Also since you'll be writing more code to setup how your game works you'll have to make more decisions that can impact performance.
As far as size, the resulting program file size would probably smaller I'd imagine.