You shouldn’t expect Kingdom Hearts III and Final Fantasy XV to release anywhere near the same time.
While talking to IGN, KH producer Shinji Hashimoto said that having Tetsuya Nomura be the director for both titles will have an impact on the games.
“So at E3 this year we announced Kingdom Hearts III and Final Fantasy XV,” he said. “Both have Tetsuya Nomura as their director, so we can’t create these two big games at the same time.
“It’s a difficult job, as we want each game to be perfect in terms of quality.”
It is unknown how far along both titles are, although FFXV had been in development previously under another name.