Final Fantasy XV was initially a spinoff set in the Final Fantasy XIII universe. Dubbed Versus XIII, this action-centric side story was supposed to build upon the foundation first set up by Lightning's initial adventure.
However, now that FFXV is an entirely new entry on its own, the crossover between FFXIII and this next-gen JRPG are minimal, but still present. Speaking to IGN, FFXIII trilogy director Motomu Toriyama explained:
You must remember, it was a long time ago that we named those three games: XIII, as well as Versus and Agito which we now call Type-0. Obviously those three projects were going to be developed against the backdrop of this Crystal trilogy, or Fabula Nova Crystallis. But each project has a different set of characters and they’re set in different universes and worlds.
When Etro is mentioned in the context of XIII and XV, we’re referring to the same goddess of Death. It’s the same goddess, but how she’s featured, how she appears and how she’s involved with the story is completely different. They’re different stories and different projects. So while it’s the same character, her involvement is very different.
Do the ties to FFXIII, even though they appear to be really loose, sour you on Final Fantasy XV at all? I know many gamers aren't huge fans of Lightning's adventure.