If i should say my opinion, all under <15 million predictions are just crazy.
Pokémon XY first year sold almost 12 million, and right now is still selling a lot (before Pokémon GO) which mean will sell at minimum 16 million, probabily 17 million.
I don't know if people realize that there is a big chance that Pokémon MS first 2 months can be bigger than XY lifetime. And is not only because of Pokémon GO, in general, userbase is bigger and Pokémon brand is stronger than years ago. But i think you will see this holidays, this game is gonna do crazy. 
15-18 million range is very pecsimist.
EDIT: Also yeah, just another thing which don't mean much but still is a good sign, Pokémon MS is already at #21 and #22 in the yearly sales, and there is still a month and half before release. The beta is not even out yet. Both will chart in TOP 10 at least by end of year (XY were at #17 and #21).
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