For arguments sake we'll assume both games get released on XBO and PS4, say within half a year of each other.
Which do you expect will sell more and how much do you think they'll sell?
In Japan I think FFXV will be a lot more successful while in America I expect KH3 to sell more. Europe doesn't really care but that could go either way, perhaps more so towards FFXV.
Both games I could see selling 4-5 million. Though I think FFXV has more potential to go higher so I think that could do better.