You need a TPMS programer. Small little hand held device similar in size to a key fob.
You can get one from your dealer for about $15 - $20. Unless you can borrow one.
Takes five minutes.
I have been looking at the Weld RT/S too for my Bullitt and if I go with them I think this is the sizes I want:
Front
Wheel Size - Front: 15x8.25
P/N: 71MB508A55A
Pad Height: Medium
BS: 5.50”
Bolt Pattern: 5x4.50
Rear
Wheel Size - Rear: 15x10.25
P/N: 71MB510A75A
Pad...
Many are using the MT Sportsman S/R 26X6.00R15LT for that size wheel.
The next larger diameter MT would be the 28X10.00R15LT, but you would require at least a 15x7 wheel.
What tire are you running in the rear?
You could go with 15”x10” RaceStars with 28x12–15s MT DRs for the back.
If you have an hour there is a sticky in this forum that addresses the different wheels and tires for 15s.
Combined 15" wheel Fitment Thread