Does FileVault 2 encrypt keys in sleep mode?
I don't believe any extra encryption is specified for the keys and also want to disagree with the statement "only parts of it are decrypted" as the entire volume is either unlocked or locked. For the filesystem to be mounted - all of it is unlocked.

So, you could enable destroyfvkeyonstandby being sure to also disable power nap since that causes restarts if the machine wakes up too many times to find that the filesystem is encrypted while it tries to run.


https://derflounder.wordpress.com/2014/02/12/power-nap-power-management-settings-and-filevault-2


For me, the risk that somehow the RAM will be captured from a sleeping Mac isn't worth the delay every wake of having to unlock the volume. My suspicions are that Apple has implemented the unlock in a way to make it highly secure whether the Mac is sleeping or not so that even if the contents of the drive are captured, you still need the proper password to unlock the volume the next time it is locked.