I looked at the 2015 Limited specs, only cause we have a 15 XLE, and see the Limited has heated seats.
My hope is the XLE has the same wiring in place, just not the heating elements and the dash controls.
My 2011 Tundra SR5 has the exact same wiring as the Limited or Platinum, but no heat elements/dash controls
making heated seats a plug and play modification. I added the glass break sensor and hood sensor
and it all was PNP.
I have a 2013 XLE. Wiring for seat heaters behind the dash. Fuses for the seat heaters were installed at the factory. I traced the wiring to the union connectors under the kick panels on either side of the driver compartment. The wiring stops there. You could buy the connectors to make a harness for maybe $25 + wire. Seat heater switches run $50 a side new. Seat heater pads are $450 per seat new. You'd have essentially factory seat heaters. Maybe better quality than the Ebay/Amazon kits. But f you can't get the parts used. it's not cheap.