As a player who played every single FIFA game since 94 and many PES games, I would say this is the most "decent" FIFA game that I've ever played, to keep it short:
Cons:
-The UI is horrible! absolutely terrible, it's downright disgusting and humiliating, no full team sheet in team management page, and what the hell is "quick subs"??? So if a player is say, a RB, and you want to switch him with a CB just to finish the match, you have to go down and handpick the sub player, which makes the "quick sub" feature obsolete... The ridiculous scouting system is still on in career mode, seriously if I wanted to use a scouting system and search for players, I'd play FM, not FIFA...
-The goalkeepers... oh dear lord the goalkeepers, they might as well be replaced by scarecrows or potato sacks, cause they... well they don't do much, tip the ball to corner on high balls even if they are not standing on the goal line, I even once seen Mignolet high punch a high ball while he was standing at the penalty spot... all alone! so aside from the "cool" ish animations goalkeepers need to improve.
-The ragdoll physics work better than 14 but the refs are unforgiving, they can show red cards for no reason, I think the "endangering" tackles are not judged quite accurately by the AI...
Pros:
-The diagonal high balls are working a bit better, the ball feels like it has weight and does not fly like a balloon, the AI is tad bit better at through runs, but the full backs still don't run as often as I want them to, which can only be adjusted in the OPTIONS... yeah not team management, options... also the marking distance of the defenders can only be adjusted in the OPTIONS... way to go EA...
-You can also get past players more easily now with only the left analog stick, that's a welcoming addition but I've never tried in higher difficulties since AI becomes a football God and plays like you're against 11 Messis...
Aaand the biggest con is that the game runs absolutely RUBBISH on PS3, it is poorly optimized and not suited for PS3, stutters, looooooong loading times, poor graphics and frame rate drops are constantly there, so if you're a PS3 owner and want a smooth 15 run, that'll not happen...
All in all if you can buy it like for 10 bucks, go buy it, otherwise it's far from deserving a full fledged price tag...
EDIT: I am terribly sorry but this review was issued before I started playing FUT or namely the Ultimate Team... The reason I chopped off 1 more point is because EA decided to ditch out the older consoles and hung them out to dry, in the FUT the game goes worse, the servers are barely working and you get disconnection issues, which means you will lose games and your DNF (did not finish) multiplier, which is a multiplier calculated for your coin wins. The individual player instructions in the game are nonexistent here (unless they patch it but I seriously doubt it) you can't customize your formations, cannot give specific instructions unless ingame in 30 seconds in pause screen (though I seriously doubt if that works either), and from time to time the game directly IGNORES your team squad, lets you play with the squad that you've played 1 or 2 games before, I've seen many times that I've changed my squad, only to see that I'm playing with the players I've placed on the bench or reserves! The game runs a bit laggy as well but I'm not 100% sure it's the servers, it might just be my connection as well...
So my point stands, for a new installment in a franchise it's not worth more than 10 bucks, especially if you're playing on older consoles since EA decided to say "f*** you ps3 and xbox360 users, go play with this beta" and give us this half finished game...