Ocarina of times is the bigger Zelda game ever, which sold 11 million LT.
Twilight princess is the second, will eventually break 10 million soon with the Wii U version.
I think will depend if this game will get a remake or a remastered after 7-10 years of release.
But yeah, it's gonna be fucking huge. 7-8 million withouth remake Wii U + NX.