A: Yes. Open SuperSU > Settings > Full Unroot. Then flash stock firmware (Android 5.1.1) via Odin.

Now that TWRP is installed, you can flash the root file.

Connect your phone to the PC via USB. Odin should display "Added!!" in the log.

on Android 5.1.1 typically requires a computer, the Odin flashing tool, and a custom recovery like TWRP Essential Preparation

If any link is broken, search XDA Developers Forum for "SM-J320F root Android 5.1.1".