Over a week after the Android 5.1.1 update started rolling out to the Galaxy S6 and S6 Edge units on T-Mobile, the US Cellular variants of Samsung's latest flagship smartphones have also started receiving it.
The OTA update is currently rolling out, so you should get a notification soon. However, if you're feeling impatient, you can always manually check for it by going to Settings -> About Device -> Software Update. Alternatively, you can also get the update by using Kies, Samsung's desktop PC companion app.
It's worth mentioning that the international versions of the handsets have also started receiving the update - the S6 is getting it in France, while the S6 Edge is getting it in the UK.
Source | Via