What if Zelda Breath of the Wild was released on Wii U in 2015... What would change?

[PAOerfulone]

Ehhh.
Wii U would have sold better for sure, but not enough to be respectable or for Nintendo to care, which is why delayed all this time to put it on the Switch in the first place. It would've taken it from the 13.5 million number it is at now, to around 17-19 million at best, assuming the 4 million people who bought Skyward Sword were holding off on the Wii U, specifically until Breath of the Wild came out in 2015. And even then, that's STILL worse than the GameCube.
I still think we'd be getting the Switch this year, but not until the holiday season as opposed to March 3rd, and I do agree that Super Mario Odyssey would've been its launch title.
I still think that games like Xenoblade Chronicles 2, Splatoon 2, and Fire Emblem Warriors would still be going to Switch, but they wouldn't arrive until 2018. This year, instead of the new Switch titles we're getting, the 3DS would be a much bigger focus. Instead of Mario Kart 8 Deluxe, we'd be getting a Splatoon pack as the 3rd Mario Kart DLC pack for the original version on Wii U, meanwhile Nintendo is hard at work with Mario Kart 9.
And that's just about all I can think of at the moment.