I had the opportunity to attend ALA Midwinter as a member of the ALA VRT Notables Committee, we voted on the most notable documentaries of the last year. Here is the list. Besides the great films on the Notables list, I also highly recommend the following docs of 2015:
Citizenfour
1971
Citizen Koch
Many thanks goes to the VRT Committee member and chair, Wendy Highby.