I may have a solution for you, but there is not a tail light that has those exact dimensions. However, if you've measured from the mounting holes on your existing lights, the Bargman # 47-54-001 might be the best option since the mounting holes are 14-1/2" apart and the overall dimensions are close at 15-7/8" x 2-1/4".
The only other option that is close would be the LED Tail Light for RVs Under 80" Wide - Stop, Tail, Turn - Weatherproof - 20 DIodes - Red Lens # DG52435VP, which is 12-3/4"... view full answer...