You're on Marshmallow, this ROM is Lollipop. You can still run this ROM but you should downgrade to Lollipop OK1 in order to follow the OP install instructions. Read the install instructions carefully; it's recommended to backup your internal memory keepsakes and wipe it. You could do this before and after stock tar but keep reading to determine if that's what you want to do.
Some may say the very least you should do is downgrade the bootloader to OK1 so you're not losing Wi-Fi connectivity and camera focus. But I only used bootloader downgrade method to restore an existing backup.
Best to follow OP for maximum compatibility.
You can backup your current partitions with TWRP in case you want to return to Marshmallow with TWRP and the bootloader upgrade method. If installing TWRP, just know that flashing a full stock tar will require installing TWRP again. The TWRP thread is in the original development thread for Sprint Note 4. Follow install instructions carefully so stock recovery doesn't restore itself after fishing TWRP. Numerous duplicate posts instruct users complaining of the issue.
There's a bootloader baseband thread in development forum for Sprint Note 4. You'll find the stock tars with md5 for verification in the general thread for Sprint Note 4. These threads could be helpful to easily downgrade or upgrade with TWRP backup restore or having a quick download when flashing full stock tar.
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