By way of IGN, we have a 20-minute gameplay video of the just-announced Final Fantasy XV: Pocket Edition from PAX West 2017.
Final Fantasy XV: Pocket Edition will feature the main characters and story of the console version of Final Fantasy XV, using an art style and casual touch controls which are optimised for mobile devices. The main story is told through 10 episodes, all of which will be available at launch. Before you decide to make the jump, the game will offer the first episode for free, so you can see if it is to your liking. No concrete release date was provided, but it will launch later in 2017.
From what we have been able to gather from the gameplay video, the mobile version of Final Fantasy XV is more or less the same as its console (and eventual PC) counterpart in terms of story, with some gameplay elements refined for a smaller screen. If you are a fan of the series, you may want to check it out.