Hmmm...yeah, sounds doable. I think XC2 did slightly more than that lifetime. This is one of those situations where I could see XC1 either far underselling or far overselling this amount.
-Highest rated game in series
-Improved graphics and extra content
-Already sold about 1.5m to a built in fanbase (Wii + 3DS).
-Switch is a popular platform and seems to boost software sales
-Bigger install base compared to XC2 release
-Corona is boosting sales
-It's a port.
-XC2 didn't sell this fast and during a December.
Overall, I think the plusses outweigh the minuses. My guess is that it can do it, but who knows?