Light orange colored disk traveling at rapid speed and low altitude.

Sitting at a left-hand front window seat on a scheduled B737 United flight from EWR to MIA around 13:45 local time.
 Shortly after departure, whilst tracking South South-West and climbing through approx. 15,000 ft, I was gazing at the terrain of the Wharton State Forest, NJ when I saw a light-colored orange disk traveling from south to north at an extremely fast, constant velocity and low altitude (perhaps 50 to 500 ft above ground level).
 In my field of view, it traversed the window from one side to the other within 2 seconds.
 It’s difficult to estimate, but I would say the disk was approx. 100ft in diameter.
 Shortly after the sighting, I saw a few general aviation aircraft flying in the area. Knowing they cruise at approx. 2nm per minute, they were extremely slow-moving compared to the orange disk. This helped validate the unusual speed of the object.
 For the record, I am an Airline pilot with 17 years’ experience flying turboprops and wide-body jets in all but one continent. This is the second UFO sighting I have witnessed. The first being over the Siberian Plateau in 2013 from the flight deck of a B777.