Final Fantasy XV is roughly half-done, according to comments by new director Hajime Tabata. Speaking with Game Informer, he noted that "about 50 to 60 percent of the game is complete". It's worth noting that he gave a specific figure of 55 percent in an inteview with Kotaku.
To be clear, this isn't half-done after nearly ten+ years of work, back when the game was announced as Final Fantasy Versus XIII in 2006 when Tetsuya Nomura was its director. Rather, the figure is from two years of work after Tabata joined the project as co-director - he's now sole director on the game after Nomura went off to focus on Kingdom Hearts III.
And if you put two and two together, that just so happens to be around the time when it was first reported that the game known as Versus XIII was canned by Square Enix. Kotaku's 2012 report also said that assets from Versus had gone into another number FF game. As we all know, Versus was rebranded to XV at E3 2013.
That tidbit is further confirmed by a just-published interview from Famitsu: former Square Enix CEO Yoichi Wada asked Tabata and the Type-0 team to help out just as the direction of the game, its platforms and its name changed (more from the Famitsu interview should be forthcoming on here in due course).
"I joined the project about two years ago, and around that time, we changed platforms," said Tabata to Kotaku, referencing the generation swap to PlayStation 4 (and Xbox One) from PlayStation 3.
"We re-examined Final Fantasy XV's development structure. We had the gameplay team, the cinematics or CG team, and the game engine team. And we finally merged them all together to work on this game. I think we can deliver the best that Square Enix has to offer."
On the near ten-year wait for the game, Tabata added: "We are making this for the gamers who have been waiting since the game was Final Fantasy Versus XIII. But, this is not the exact same game. The director is different, and the platform was switched to the current gen. And because the platform has changed, there were things we had to re-evaluate, like what we can and cannot do or even what we have to do. The various circumstances are different."
A demo for FFXV, Episode Duscae, will come with Final Fantasy Type-0's release next Spring. A date hasn't been confirmed for its launch, although Square Enix has said it's aiming to have it be for Type-0 HD's launch or close to it. Here's its TGS trailer and demo respectively.