I think you are overestimating the influence of internet hype and bundles on sales. I don't see any particular reason why this game should break 20m. I'm a huge Pokémon fan, mind you! But so far there is only anecdotal evidence (people telling their subjective feelings) and I see no hard numbers to back the "bigger than gen 2" claim up.
Also, bundles won't make a big difference as they are usually very limited. I don't see any reason why the game can't sell 15-20m but I don't see any evidence pointing to 20m+ or a minimum of 16m. I hope it does well, though.







