I'd be quite surprised if it did better than the first game to be honest. I haven't seen it selling to new audiences and a fair amount of people who bought the first game aren't interested in this.You need to take account a lot of people get into Destiny after TTK... these are now day one buyers.
D1 launched at over 5 million units WW from 0.
D2 has over 30 million players to buy the game.
Even if 20 million choose not to buy it for whatever reason there are enough players to sell way more than D1.