How to Root Sprint Galaxy S6 5.1.1 How to Root Sprint Galaxy S6 5.1.1 with build G920PVPU3BOL1?
Flash the following kernel to get root

Uni Kernel

Updating the answer based on comments.
Download latest version of Odin (Google for download link)
Turn on USB debugging mode on your phone (Google again)
Install Samsung USB drivers (Locate your phone on Samsung support site to download)
Restart the phone in download mode. Connect your phone to the computer and turn on Odin
Once Odin recognizes your phone, select the kernel by choosing AP. 
Flash the kernel.