I guess they intertwined a lot. But looking back on the entire experience, I remember more about the plot than I do about the characters. I wonder how much playing the character packs changes that... I never did.
I mean, I remember key points in the plot and how they impacted the characters, that's for sure. I remember the characters being seriously central to it all. But for me, FFXIII is a better example of characters > world plot.
I learned so much about the characters in FFXV but I never really felt there was the character story to push them. They were just who they were, with a couple of exceptions. I get the feeling there was a lot of room for us to explore their characters if they just put more into the (original) game. I'll play the character things eventually... maybe. xD