Halo: The Master Chief Collection will have a 20GB day one "content update".

[Burek]

Some good news for Halo fans:

Day One patch will be smaller than expected -- 15GB!

Also, if you preordered digitally, you can already download it and be ready to play immediately on November 11.

http://www.engadget.com/2014/11/06/halo-xbox-one-day-one-patch/