There is a fair amount of judgment call in this. The specs say the truck will do it, which basically means it won't break down, at least not within the warranty period.
It doesn't say you will like doing it, or feel safe in a crosswind, or not soil your underwear if a driving emergency happens.
Another factor is that the truck specs are NOT tuned for RV trailers only, and RVs are harder to tow than low utility trailers. RV trailers have high frontal wind resistance, high center of gravity, and are very susceptible to sidewinds, so it's better to stay below the maximums. If you were talking about a 250 or 350, they are designed for heavy hauling. A 150, though, is designed and equipped more like a passenger vehicle with a big open trunk. Tradeoffs are made for ride comfort and fuel economy rather than handling big loads.