It's 15. Looking at the newest wave of Campaign previews, some sites say the Locke canyony mission, titled [spoiler]Swords of Sanghelios[/spoiler], is two thirds of the way into the Campaign.
Other sites have said it's the tenth level. So my meagre arithmetic abilities tell me that puts H5 level with H2, ignoring intro cinematics and training 'level' Armoury, at 15 playable levels.
So, another H2 split? 8 levels with John and 7 with ... Wait. Was H2 13 playable levels?
H5 bigger than H2's space opera confirmed.
-
Well though it means very lil number wise the game is supposedly 2-3X longer then Halo 4. I'd say make each mission half as long as your usual Halo4 level and that will be about the length of the average mission in 5 so say a mission at a moderate run through of 30 mins (stopping to kill almost every enemy etc) and halo5's average mission length could be up to 45mins-1 hour. Either that or we will get roughly 20, 30 min long missions.