I have a 2015 macbook and have been running into similar issues. I have had it for about 5 months. I've reset SMC once, but am not convinced the other recommended actions will make any difference, as wake time is random.
At this point, as an experiment, I have disabled blue tooth b/c I have no need for that connectivity. My machine has a screen saver and file vault enabled. At home I have rather old airport as wifi-base and time machine backup (half suspicious an interrupted backup is causing problems).
System Version: OS X 10.11.5 (15F34)
MacBook (Retina, 12-inch, Early 2015)
Waking from sleep is problematic. It may be instant, 20 seconds, or 5 minutes or longer. Infuriating can only begin to describe this situation, as I have no idea if I have brick or can do work when commuting. I may work on my machine at home, close the lid to fetch a coffee and work a bit from whatever coffee-shop only to enjoy my brick will drinking coffee. Or have something to do.
Or, after walking home, open the lid had have it take 7 minutes to wake. Access to power makes no difference. If I plug in power, I get a chime, but the box is otherwise dead to me and I get to wait until the device decides to power up the keyboard and screen...
Notably my old 'cheese-grater mac pro' is working on el-capitan and has no issues waking. I'd rather not try to use this as a mobile device.