I think so

Xenoblade 2 made 1.7 million in 15 months and the first game is a classic, this one has a clear shot to 1 million+ in one month and I'm totally into this prediction

The best part of this release is that Nintendo is no longer holding back the sales potential of the game (limited release at Gamestop only when it came stateside). The unfortunately part of this release is that the pandemic has been a thing. Of course, digital sales are not affected by COVID-19. Not to mention, I'm sure Nintendo produced a decent amount of the limited editions, which adds extra revenue.

Hopefully, XBC DE ends up selling really well. It basically had Okami syndrome, a critically acclaimed game with not a lot of sales success.

Pah! It will sell 100 billion units!

I will be in the negative side because I think that is most likely. But I'd like to be proven wrong big time!

Sure, I could see the game having shipped 1,5 mil at the end of June, and while that's not quite the same as sell-through being 1.5 mil, it's probably the closest we can get to confirmation of this.

Honestly 1.5 million for the game in it's first quarter is a stretch. Not impossible, mind you, but ~1 million is more likely. X2 came out at a time when there weren't quite as many games on the Switch so that probably helped them. Oh, and reviews could also have an impact on this.

Seems possible but how would we know?

It is surely possible and the even more skyrocketing popularity of the switch this year will also play into this.

In july Nintendo will have their quaterly report.

It could reach two million in a lifetime.
But I think 1.5 million is impossible in a month.