I was under the impression that Battlefield 4 sold well below that. Probably about 3 million each on PS3/360, and 1.5 million each on PS4/XB1 (a very generous estimate given the NPD numbers by creamsugar). And let's add in another 1 million on PC (though I suspect it's closer to 750k).
That means BF4 sold ~10 million units worldwide. It's possibly as low as 7 million (see this for reference -
http://bf4central.com/2014/05/battlefield-4-sells-7-million-2-still-playing/). Admittedly, Battlefield 3 sold considerably more (15 million by June 2012 according to EA's official press release) but I don't think we should take that number as a baseline. Battlefield 3 was a novelty at the time (in terms of stunning graphics and CoD-esque gameplay that wasn't Call of Duty), and I would guess that they won't be able to recreate that success anytime soon.
Having said all that, though, I'd expect about 1/3 of the people who bought BF4 to buy the spinoff. Franchise fatigue has already set in for the series, and I suspect a large number of the PS4/XB1 purchases were related to lack of launch titles. I also believe that the terrible bug-ridden state of the game at launch hurt the brand.
So I expect about 3 million units. I'm unsure if that makes it worthwhile for EA.