How can you make a Mac (2015 Yosemite) hibernate? (Hibernate like Windows PC, ie. save state to disk and fully power down)
"Sleep" and "Hibernate" on Macs aren't separately choosable. If you sleep a Mac and then leave it asleep on battery until the battery gets low, it will go into "deep sleep" (Apple's term, it's essentially Hibernate) and save battery. On older Macs that supported this, you could force hibernate by pulling the battery out, but that's not possible anymore.

Here's Apple's documentation on Mac sleep, scroll down to the section on "Special Sleep Modes". It may be that the "standby" indication you are seeing is exactly what you're looking for.