The math doesn't work.
$7.6 billion, even if you assumed $100 price tag, would be 76 million copies sold . More likely is the $80 price tag in which case they'd need to sell close to 100 million units in the first 2 month to hit that target.
GTAV sold 29 million copies in its first 6 weeks. Which means this would have to sell at about triple the pace of GTAV. Has any franchise tripled its sales from the previous installment?
I have no doubt GTAVI will break records and will eventually get to $7.6 billion and beyond. But I think to do that in 60 days is a bit over enthusiastic.