If it's ready they'll release it.
If it's not, I don't think they will force the issue. They may even reposition it as a Wii U + Fusion launch title just like Twilight Princess if it slips to 2016.
They can slide Pokken Fighters in or move Splatoon and Xenoblade further into the fall if it can't make 2015.
There's no real crushing pressure on them with the Wii U anymore, it's going to go down as a relative failure with or without Zelda in terms of being a fair lock as their lowest selling franchise.
So they may as well make sure Zelda is the best game possible, there's no point in rushing it.
A non-Zelda 2015 I think would look probably like this:
Jan - Nada
Feb - Mario Party 10
Mar - Fatal Frame V
Apr - Yoshi's Wooly World
May - Mario Maker
June - Super Mario Galaxy Collection HD
July - Devil's Third
August - Kirby's Rainbow Curse
September - Xenoblade
October - Splatoon
November - Pokken Fighters Tournament
December - Star Fox U







