On mine, it's fifteen feet 4 inches.
But, what is more important is the center of weight compared to the length to the hitch. This determins how much weight will be on the hitch. The longer your trailer is (center of weight point or center between axles to the hitch) the less the weight will be on the hitch. Think of it being like a lever.... the longer the handle on the lever the less force is needed.
I'm loaded a little foreward of center because my trailer is pretty long.
You want the weight on the ball to be close to 500 lbs. Anyway on my truck, that's about where the big springs start to kick in and the truck rides best.
Oh.... and yes, she is pretty .... but even pretier in the water