Maybe update via Kies using a PC?
Firmware for Samsung SM-P905V - SamMobile
Wish I could walk you through it but it's not something I do (I'm on a wifi variant and use custom ROMs insead).
BINGO!
Went to the SamMobile link above.
Here's a summary:
On PC
Download, extract, and install Odin through link at SamMobile
Download and extract the firmware file at SamMobile. Note, You need to sign up with SamMobile before you can download. If you don't pay for a premium membership, the free download will take about 2 hours.
Open Odin
On Tablet
Reboot in download mode per instructions. You should see Mr. Android and warning "Do not turn off target"
Together
Plug tablet into PC.
You should see an entry pop up on the log in the lower left corner of the window.
Click on AP and browse to the firmware downloaded.
Click on Start.
You should see entries pop up in the log. A bar will grow on the tablet. A rectangle in the upper left of the Odin window will have corresponding growing green.
When done, that same rectangle will say PASS.
Upgrade is great. I can now load Peel, the replacement for the defunct Smsung Watch On.
Thanks. That wasn't as bad as I thought it would be. With Odin on my PC, it should be relatively easy to upgrade to Marshmallow when it comes out,