From what I've read apparently it will be the whole beginning of it, around 90mins of the game, I don't think they're editing it but they haven't really gone into any detail about it so who knows 
Chances are between the demo and release date a lot of things would be tweaked for better performance when the full game is released.
Chances are between the demo and release date a lot of things would be tweaked for better performance when the full game is released.