I haven't played many 2015 releases -- off the top of my head, just the Concordia Salsa expansion, Codenames, and Blood Rage. Checking BGG, I see also that Antike II, Fief: France 1429, Galaxy Command, Power Grid: The Stock Companies, and Seven7s were released in 2015. Of them, I'd say that Concordia: Salsa is my favorite, but that's not really saying much.
My most played games last year were One Night Ultimate Werewolf (by a huge amount), followed by Tsuro (filler while we wait for people to show up) and Coup (which fills much the same role as ONUW, but is more/less enjoyable for certain people). I didn't play any single big game (Agricola, Antike II, BSG) more than five times, except for Concordia.
The Gallerist, Food Chain Magnate, and Race for the Galaxy: Xeno Invasion were the 2015 games I most wanted to try but didn't. I expect that I'll buy Xeno Invasion once the corrected reprint is out later this month, but I'm not ready to put down cash for the other two, as I doubt I'll have the opportunity to bring them to the table with any frequency.
I purchased two 2015 releases that haven't yet hit the table: Tiny Epic Galaxies and Valley of the Kings: Afterlife. I hope I have the chance to play them soon.