The point is that Frozen hasn't peaked popularity. Hell, Toy Story 4 and The Lion King (2019) passed it recently. It's the 8th highest-grossing animated movie domestically when it certainly doesn't feel like it as shown by blu-ray sales. There is ton of room to increase in growing markets, even if it doesn't feel significant. If you remove the OS grosses from Despicable Me 3 and Frozen, Despicable Me 3 is actually ahead of it overseas. I don't believe that there is any other prospect to show how big Frozen 2, and there's like 1% chance it reaches $2B. $1.6B ($310M + Frozen) seems about right, especially if Disney doesn't disappoint its audience.