The updated model is the Samsung Galaxy S6 SM-G925T corresponding to T-Mobile. Although the SM-G925F corresponding to the global version is also ready.
Samsung changes are a new guest mode, better exposure in the camera, parallax effect on the wallpaper and multiple interface changes and the performance has been improved with the arrival of Android 5.1.
The update is available via Samsung Kies, although Spain does not yet appear. We will update this article when the OTA is available for download. For now we leave the video where SamMobile makes a brief look at the changes seen in Android 5.1 Lollipop for S6.