Can't really judge the two when FFXV isn't even released yet. We barely know if the story will be any good. I believe it will. Less of a political story than XII. That's already a win in my books. I only played FFXII because there were a few good characters, but the highly political and I despise anything to do with politics. So it was a complete cluster**** in my opinion because I barely understood what the hell was going on and why the countries were at war.
FFXV already seems way better and more understandable than XII. Nomura even said the plot is simple. The last crystal in the world is stolen from Lucis Kingdom. Noctis and Co must retrieve it at all cost. That's it. What happens in between is all just part of telling the story that leads up to the climax of getting the crystal back finally.
Stella will be playable in Final Fantasy XV. Calling it now. Official Conductor for the FFXV Hype Train