Anything can disappoint. There is always that chance.
Having said that, FF15 has a lot of good things going for it. It hasn't really been in development that long. Due to the inept management team behind FF13 and the incompetence of Toriyama, as well as the FF14 disaster, the team behind FF15 wasn't really a complete one until recently. They've been pulled apart here and there to help with other problems.
As it stands, by the time the game does release, it will have been in development 2-3 years past the preparation stage. That's a good amount of time. FF13 had half of that if I remember correctly, and that was after a very poor concept stage where they didn't know what they were doing, or where to go with the gameplay. An added benefit for FF15 is that the team has had a lot of time to prepare to ensure their vision is focused for what it needs to be. The troubled development time is exaggerated. That has little to do with the team behind FF15. It would be more accurate to say the troubled development of FF13 and FF14, along with SE becoming clowns, forced this game to be delayed.
Whatever you receive, at least it's not a rushed product. There is a focused product, and a clear aim.
Lastly, the talent behind the game is pretty damn strong. You have Nomura who has put out some quality games, Nojima who birthed the initial concept of the mythology being used, Yoko Shimomura on the OST, and a bunch of other talent from previous SE projects. It also helps that Nomura is aiming for a Kingdom Hearts style system so he has experience which will help deliver something solid on that front. Add in the fact that we have an actual world this time, rather than just hallways, and there are more positives than negatives.
Quite frankly, there is no chance it could be as shit as FF13. There is nowhere but up from that point.