Yeah just saw this.
I found this graph for NPD results:
I trust VG Sales way more than VG Chartz, just FYI.
Anyway, if this is accurate and what Mat is saying is accurate, then Xbox Series sales in NA right now are probably ~ 14.5 million at least, going by his "slightly behind" (I think anything greater than 500K would be more than "slightly" but that's maybe just me). It could be 14.8 million or 14.9 million in NA though, who knows.
What is a bit interesting in that case, though, is that the U.S might account for just 20% of total Xbox Series sales. I figure Xbox Series was at ~ 26.2 million by end of March, and I doubt they have sold any great number of systems since then (a safe guess for current figure would probably be something like 26.6 million). So assuming they're only "slightly behind" Xbox 360, something like 14.8 million in the U.S seems possible.
I'm curious how much Canada, Mexico, Brazil and the UK contribute towards total Xbox Series sales though; they are kind of the only other major territories for Microsoft.