Is it possible to return to the Lucis that takes place in Chapter 14? (potential spoilers)

In the chapter 14, before heading to the Kingdom of Lucis, Noctis

finds himself in a world covered in darkness and overrun by high level daemons.

When I first came to this part of the story, I was not strong enough to fight these daemons and was forced to continue.

I have since beaten the main story and completed the post-game content in chapter 15 and my character's level has increased to a point where I have a chance against the daemons within chapter 14.

Is it possible to return to the Lucis where Chapter 14 takes place?

According to a post in this thread, no, you cannot return to future Lucis.

Nope. After you beat the game the game makes you create a save file for future use. You are then sent before the fight with ifrit and from that safe room you can use umbra to return to the past. Future Lucis is not an option.

I believe that this save file is beyond a point of no return, which means you won't be able to leave the area and return to open world future Lucis.

That said, I haven't seen any evidence of there being sidequests in Chapter 14's future Lucis, though, so I don't think you're really missing anything.

Since there isn't a way to do so in NG, the only way for you to fully explore future Lucis would be to progress your NG+ file to that point. Since you retain levels, you won't have much need to grind in order to stand a chance against the high level daemons.

In the recent update version 1.14, a new chapter select mode has been implemented once you have completed the main story.

Version 1.14

• Implementation of a chapter select (available after completion of the main game)

This feature will allow you to select and re-play through any chapter in the game while keeping your characters levels and inventory.