I wonder if you could get an earlier year Kook at the same price?
I'd be going for the oldest year I could..unless you personally like the 2015 or feel it will have a better retun numismatically.
Ultimately, I would be searching ebay/dealers/market for 2012 kook vs dragon, 2013 kook vs snake, 2014 kook vs horse etc...see what the trend says..