I went with 1.5 mil. It's launching fairly early in the Switch's lifespan, there aren't a lot of competitors on the market for it, and it's a dry time for 1st party efforts from Nintendo. The fact that they seem to have incorporated so many new modes will also help.
On a side note, I think it's crazy that Nintendo would keep pumping resources into such a poorly selling franchise. Certainly it seems to have sold well a few times, but not enough to warrant such a consistent flow. This should make fans of the franchise happy. Personally, I've never heard of anyone being excited about a new Tennis, Golf, or Strikers game from Nintendo, but whoever you are, thank your lucky stars that Nintendo loves each of their franchises like they were its only child (except for Chibi-Robo and F-Zero, of course).