Travel trailer axles are proportionally closer to the middle of the trailer body than a utility/cargo trailer like yours. With the axles further to the rear, less tongue weight is necessary for a stable tow, especially with the trailer empty.
Empty is as evenly loaded and as low of a center of gravity as the trailer will ever have. RV trailers are often heavily biased to one side or the other due to the kitchen being along one wall, and their center of gravity is much higher.
You are not disproving any laws of physics here. Rules of thumb are hardly absolute, and the 10-15% rule is just a rule of thumb.
What you will find is that as you load the trailer, the tongue weight will probably end up well over 15%. This is not a big deal either. There's only so much space in the trailer and most of it is between the axles and the truck.