Got a source for that second figure? If so I'll update the sales on the game page - https://www.vgchartz.com/game/80977/the-last-of-us-remastered/?region=All
Last update we could find when adding the series' sales was 8.15 million for the PS3 version and 11.78 million for the PS4 remastered version.
Edit - I think you've just misremembered what the 20 million announcement was for. It was for both versions combined, not the PS4 on its own.
Yes, combined with TLOU:R sales are 20m.