I have a Galaxy S6 Active and I use T-mobile.  To get the OTA updates I've been borrowing a friend's AT&T SIM.  However, I've also read that you can apply the updates using Odin.  My understanding is that the Odin route wipes data, so I went the "borrow SIM" route.  
If I'm wrong and there's a way to apply the update without losing data, please correct me as I'd like to know that as well. :-\