While I think this is possible, this time I have to say I think people are over optmistic. Most are saying that it will do it easily, others even saying stuff like 20m+... is quite shocking to me. The majority of sales come from Japan, and so far Switch has been underperforming there compared to the 3DS (and DS obviously). Sure, this can change once games like Smash, Pokémon and NSMBUD hit, but it wouldn't need only that, the game would also need to comfortably surpass their predecessors in Japan, and I think this is quite hard as they usually do 5m+ there, which is already near the high end of what a game can do in Japan.
Other than that, the rest of the world was responsible for "only" about 6m of New Leaf's sales, so it should do 10m+ outside of Japan alone just to be able to surpass 15m. Anyway, I'm positive most of these things will happen, I just don't think it's that clear or easy as some as making it sound.
AC has rising popularity in West also, talking about Japan specifkly, Nintendo games generaly sales better in Japan (and in other markets) then they did on DS and 3DS in same time period, also Switch sales in Japan will really explode when we get price point of around $200, and for end, AC is type of game that will sale hole generation.