60 mil or more.

i think it will stay 5 to 1 and therefor 40 million more but depends how all handheld sell overall

I 2nd this, though i don't think the Vita will quite reach 15m (i'm expecting Sony to stop production before it can slug its way there).

i guess 50 million but it could be more, it depends on how long the 3DS stays on the market without getting a true succesor, maybe the NX? who knows we have to wait and see what that "thing" actually is.

65m, less than ps4, wiiU gap

65m vs 15m
So there'll be a gap of 50m.

80,000,000 for 3DS and 15,000,000 for Vita.

65,000,000 gap imo.

3DS - 65-70 million

Vita - 13-15 million

So quite a considerable gap, ~50 million. I doubt Sony makes another handheld, especially considering the Vita has been pretty much abandoned by them.

Id say about at least 50 mill gap.

The Vita is essentially dead, only able to sell a small number of units per year, and lack of 1st party support.
While the 3DS is slowing down but will still sell more per year than the Vita.

3DS, 65-70 million
Vita, 15-20 million

So about 50 million