AT&T has finally begun rolling out Android 6.0.1 to the Samsung Galaxy S6 and S6 Edge. Other carriers, including Sprint, Verizon, and T-Mobile have already begun pushing out the software update, so it was just a matter of time until the big A started to do so as well.
Updates in Marshmallow for the Samsung 2015 flagships include UI tweaks throughout the system, new emojis, Google Now on Tap, better battery life thanks to Doze mode, an updated Samsung built-in browser, and other features included wtih Marshmallow. Keeper, AT&T Live, and Facebook Messenger are all being removed from the software as built-in bloatware, while AT&T Mail and YP Mobile remain preinstalled however available to uninstall.
1.5GB seems to be the rough size of the Marhsmallow update for the S6 and S6 Edge. Be sure to be on a Wi-Fi network while downloading the upgrade package while also having a full battery.