Sprint has started pushing out an over-the-air update for the Samsung Galaxy S6 and S6 Edge that bumps both devices up to Android 5.1.1. This leaves each handset running the latest version of Lollipop. The OTA comes following similar ones from T-Mobile and US Cellular.
The changes should place your Galaxy S6 or Galaxy S6 Edge at software version G920PVPU2B0F7. It's the same across both devices. Altogether, you're looking at a download just under 570MB.
Sprint has updated its support pages for both devices with mention of the latest OTA, but you won't find anything of interest on the changelog aside from Android 5.1. You can browse them for yourself at the links below.