So the 15-foot - one of six models (counting the 5.0 and 5.0TA as two generations of one model) - accounts for only 10% of production... although, to be fair, the run wasn't nearly as long at some other models.
It makes perfect sense to me that the bathroom is only optional on smaller models (up to 17-foot) and is more commonly omitted in the 15-foot than the 17-foot. As one goes down in trailer size, the space taken by a bathroom becomes more significant, and people buying the smaller models are commonly limited in towing weight capacity so they are further motivated to keep the feature list lean.
It makes perfect sense to me that the bathroom is only optional on smaller models (up to 17-foot) and is more commonly omitted in the 15-foot than the 17-foot. As one goes down in trailer size, the space taken by a bathroom becomes more significant, and people buying the smaller models are commonly limited in towing weight capacity so they are further motivated to keep the feature list lean.