As previously reported, a demo of the upcoming Final Fantasy XV will be included in the HD version of Final Fantaasy Type-0.
GameInformer gives details on what to expect in the demo:
Square Enix is calling the demo Episode Duscae, and though it focuses on the early parts of the game, some elements of the progression have been altered in order to make it more suitable for a demo experience.
What players will be getting with Final Fantasy Type-0 is actually a voucher for the demo. Square-Enix did not confirm if the demo will be available the same day as Type-0 so there’s a good chance that the voucher will need to be saved for when the demo becomes available to players on both the PS4 and Xbox One. Also, the fact that it is a voucher implies the demo might be paid, which if it is would be awful but not uncommon.
We will have to wait until there are more details on the matter.