Assuming you are including people paying with tokens (hey, I have seen people claim that those are not subscribers so I am just covering my bases here) I would say 5-7. Around this point in WoD was when they gave their last subscription numbers as ~5.5M if I remember correctly, and I can't imagine Legion is doing much worse than WoD...
People saying 1.5-2m are the ones who have ALWAYS said crap like that... there were people during cataclysm that would claim that those would be the numbers in the next report.