Did you do a factory reset after updating?
Back up your data and do it. Use the Recovery Mode (Phone off -> Hold power / Vol Up and Home Key) and wipe Cache/Factory Reset.
If possible install everything fresh and don't use backups (except for messages etc of course). Especially on an Exynos model of the S7 Nougat's battery life should roughly equal or be better than Marshmallows, Snapdragon also, but since i don`t live in the US, i can't verify, since the majority of my friends and myself use the Exynos version.
Also check your apps for wakelocks and the like. Disable/uninstall apps not needed (for example if you don`t use Samsung VR/Gear, deactivate it. It will help improving battery life).
Other than that, enjoy nougat