Find the payload on the driver door as was mentioned. It will give you an approximation of what the truck can "carry".
Some thoughts; a 15 passenger van is a BUS! It was meant to carry people, not tow big RVs. Whatever the payload is, it was meant for it to be inside the van, between the axles and not hanging off the back wagging an elongated RV.
With 7 kid (growing) and 2 grownups that van will be packed; not only with people but all their "stuff". Trying to control a bumper pull trailer in excess of 38' long and 11' high would be iffy by itself. Throw a family of 9 in the van pulling that thing "hoping for the best".....
