2015? Holy shit, that's like a decade too late. Who's going to watch it at that point? The at that point 4-5 million core players (here excluding trial accounts, people owning more than 1 account, and those who plays on and off)?
Do they expect the 30-40 million players who previously played WoW with all the sweet memories but now nothing but hatred left for Blizzard for ruining the game at XXX point in time to all go watch the movie? What about all the CoD, Fifa and LoL teenage gamers who know nothing about MMOs and RPG? Or everyone else who have nothing but stereotypes left for those who plays/used to play WoW...? Does Blizzard really expect themselves to be able convince these type of people to come watch their WoW movie, a concept that slowly lost its appeal for everyone outside of the game by the death of the Lich King.
I'm sorry to say this, but unless it becomes a huge sucess then I doubt it will sell well. And if it becomes a huge sucess then I don't think it is the fact that it is based off WoW that made it a sucess in the first place.
If it becomes a sucess its going to revive whats left of WoW in 2015. If its going to become a failure Blizzard and WoW is just going to be laughing stock by non-Wow players.
Personally I'll probably watch it, together with people whom I've previously played WoW with. Hopefully it will become a succes in the cinemas of the US so we can actually have a cinematic release here in Denmark as well.