Outside tire wear is an alignment issue.  You need to fix that first.  As for tires, VF240/80R15 is the radial implement replacement for 9.5L-15 that fits on the same wheels you have.  The radial implement is a much load rating and speed rating (40mph vs 25mph) that what you have now.  We are going radial implement on all the wagons as tires are replaced as they are a far superior option.