The 10-15% applies to RV travel trailers but not other types. A tow dolly is well-balanced and the weight of the car is positioned directly over the dolly axle, so almost no weight falls on the dolly tongue. Your dolly tongue weight should be around 50 lbs, whether loaded or not.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL