Well, people say PES 2015 is just faster and more responsive PES 2014. I would not say so, but you can see and feel the same base on which both are made. 2015 have more variety of animations, slightly better collision system, obviously better graphics, and more responsiveness. Speaking of graphics, from some angles, pitch look very pale and low texture, but not a big deal. Player body models, face textures, stadium and everything looks fantastic. Fox Engine really have amazing lighting, probably the best lighting till date.
Though, 2014 and 2015 are similar in terms of gameplay, I would say. Player movements, smart defense and attack, tactical part... but I expected more from 2015.
2015 reminds somehow of PES 6. If you liked 2014 gameplay, you would like 2015 even better, if you don't mind the speed. It's much faster.