Although we are not far from the Release of Android N. But there are some last year flagships which did Not get Android marshmallow yet till Now, AT&T Galaxy S6 and Galaxy S6 edge are two of them. But thankfully the wait is over and AT&T is rolling out OTA to both Galaxy S6 and S6 Edge which contains Android Marshmallow.
The update weighs 1.5GB in size and contains all the basic marshmallow features like Google Now on Tap, Doze power management, improved permissions control, and more. Along with these there are also some changes in TouchWiz’s new look and a revamped notification panel. With this update your Phone will also update the Android Security Patch Level to May 1, 2016.
The update is rolling out in stages and will reach you in a day or two. Meanwhile, if you did not get the OTA notification than do check for update manually by going through the setting of the phone.
If you receive an Update than do share your experience after updating your device to Android Marshmallow via comments.