BOTW with the Wii U version (2m according to this site) is at 6.7m which is 1m behind OOT's total and 2m behind TP's Total and all of this is in 7 months of NS' launch and 3.3m shy of the 10m mark which I'm sure it can hit LT.
Where does it say Wii U BotW sold 2m? If you're talking VGC it's at 1.1m here now. I can't find Nintendo's numbers on this anywhere, so I'm either missing something or you just got it wrong really. Still, I recall the game being at 1.08m or something way back in April I think, so probably Switch+Wii U is around or past 6m by now, which is pretty impressive. 10m for both versions seems very likely at this point.