Only played 2013 and 2014 and both ran well for me. 2015 was on the new engine but that passed me by with so many other games released roughly the same time.
2014 was pretty decent the co op was good & online was more functional , however that being said the game had its fair share of bugs and still does to this day.
when i say bugs i mean like in both 2014 and 2015 if you incurred a penalty in qualifying when playing online once you then enter the race quit then restart you will find your penalty has gone. Loads of silly bugs like this in both games that just never got fixed they spend about 2 / 3 months using us as beta testers upon release then drop support.