"At the moment, it feels like it's at around 50 - 60%."
"We kind of started from the beginning of the game, so the first part is more complete than the others." Speaking separately with Kotaku, Tabata wanted to clarify: This is 55 percent during the two years Tabata has joined the project and the game's systems are more or less already in - there shouldn't be much of a wait after the demo is out, at least not years and years.
http://www.novacrystallis.com/2014/09/final-fantasy-xv-is-50-60-percent-complete/