As per the timetable, Marshmallow is expected for Galaxy S5 unlocked by April but it seems updates are getting leaked. 🙂 After update user has told that he have got refined permissions and Doze feature of the latest Android version is also present in the update. Also, Google on Tap is also active after the installation of the update on Galaxy S5.
Guys if you own Unlocked Galaxy S5 then you can also check it for the update by going into settings then about section.
You can check the screenshots of the Unlocked Galaxy S5 running on Android 6.0 Marshmallow.