The Samsung Galaxy S6 has been kept updated by the phone maker as they have sent out updates for the handset. Some of them were needed as the S6 did have numerous issues that needed fixing. These issues had to be fixed before the Android Nougat OS is launched for the older handset.
One of the biggest issues with the Samsung Galaxy S6 has been the poor battery life of the device. However when it does get an update to Android Nougat the operating system may be able to help with the battery life thanks to it having the resolution switch.
With the resolution switch the display of the Samsung Galaxy S6 can be reduced, which should help with the battery life. Of course the Samsung Galaxy S7 isn’t going to get benefit from the resolution switch as it offers better specs and this can help balance out the battery.
So it does look as though the Samsung Galaxy S6 is going to get more out of the Nougat update than the Samsung Galaxy S7 is.