Is that one orange? I don't have #15 but I have the #16 one, which I thought was the same colour, and I'd call it "yellow", though I've never seen the #15 in person to be able to compare it directly.
I'd call it a mustard yellow. I consider "goldenrod" to be a bit more brown/ochre....The #15 and #16 Mustangs are the same shade.
It looks a little yellowy in that pic, but it always struck me as more orange.
Like goldenrod yellow, which could easily pass for a lighter shade of orange in some circles.