Federer was up against a prime Djokovic when he himself was approaching his mid 30’s. His ground game had declined significantly and Djokovic was at the peak of his abilities. The fact is Wimbledon is a baseliner’s game now and a prime Djokovic is just a better player overall player than an old Federer. Djokovic was simply the better player in the 2014 and 2015 finals.In My Opinion Federer should have kept his grip on wimbledon as strong as Nadal kept his grip on french for 15-16 years, but then Federer allowed Novak to win 5 times and Murray to win 2 times, those slams should have been Roger's, at least 5 out those 7 he should have poached.
Sadly he could not and that is what has hurt him, on HCs I dont see a chance vs Novak from 2011 onwards though he did have his chance once or twice... but that was not gonna work.
Grass was his best shot at keeping the slams record till the end.