"We can't give too much information but certainly looking at Final Fantasy XV, it's not as if it's in competition with Kingdom Hearts 3 for resources or anything like that," Kitase said when asked about the status of those two games. "It's quite far into development now and it is being given a very high priority within the company itself, but that doesn't mean Kingdom Hearts isn't."
Final Fantasy XV was first announced at E3 2006 as Final Fantasy Versus XIII. At the time, the game's story was part of the Fabulla Nova Crystallis mythology shared by other Final Fantasy XIII titles and despite the name change, Kitase says Final Fantasy XV's story will still take place in that mythos.
Right from the start when we first it announced it as Versus XIII, the game itself was backed up by the same Crystal legend: the Fabulla Nova Crystallis mythology that underpins the whole of the XIII series...So even though it's not necessarily the same universe or the same game, they're all linked and underpinned by the backdrop of that legend. Now it's moved on - obviously the title's been changed to Final Fantasy XV - but that hasn't actually changed. The story and the world is still going to be linked and backed up by that. So yes, there is the link between XIII and XV, and they both share that mythology as a backdrop and a starting point.
In the interview, Kitase also talks about using the power of the PS4 and Xbox One to create larger battles and the possibility of returning to battle systems used in past Final Fantasy games.