We don't know, because companies tend not to brag about those sort of things. Remember how long it was until we got even mildly solid numbers on GT6 sales?
As far as sub-2 million sales, that'd be most racing games, actually. Most of the Forza games are there or slightly above. pCARS only made 2 million near the end of last year. The Codies F1 games
don't do great, and I'd be surprised if Dirt Rally or Dirt 4 cracked 2 million. Assetto Corsa isn't close. There hasn't been another racing franchise in years that has publically admitted to cracking even 3 million let alone 5, outside of stuff like Mario Kart.
Racing games are not "big" games now, even if they have major studio support behind them. It's just not a particularly popular genre, especially with shooters and action games offering more freedom, better story telling and greater online opportunities than ever before. GTS could be the best racing game the world has ever seen, and in this climate I would
still say it's entirely possible it doesn't crack 2 million.
Racing games are not the thing that they were on the PS1 and PS2.