In an interview with IGN, Yoshinori Kitase, the producer of Lightning Returns, explained that Final Fantasy XV will very much have its own unique battle system.
The two things that we put great emphasis on when designing the battle systems for all games in the Final Fantasy series are that the character’s personalities are expressed through them and that there is a deep and satisfying strategic element. Apart from that we strive not to be bound by any particular conventions and try to absorb all possibilities in order to evolve new systems. Final Fantasy XV is in no way a direct extension of Lightning Returns and will no doubt introduce completely new battles with new surprises of their own.
Lightning Returns: Final Fantasy XIII launches on February 11th for Xbox 360 and PlayStation 3. Final Fantasy XV will be coming to Xbox One and PlayStation 4 at some point in the future. Here's to hoping we don't have to wait forever.