Bought a van

[KWKENUF]

What zieg85.  You have a P rated tires.  They typically only go to 35-40 psi max.  Get an LT rated tire,  even the C load ratings go up to 60 psi max,  if not higher.  I don't think you need D load rated LT tires,  might be over kill for what you need,  and they will be heavier.  Just going to an LT tire will get you at least a two ply sidewall.  P tires are only one ply,  hence the 35-40 psi max.

[78 Chevyrado]

My brother ran LT load range C (LT215/75R15C) on his Astro when he had it

I either want 215/75R15s or 235/70R15.  the stock sizes are all 97s rated, but the 235.70R15s I found have a 107s rating.  I can't find anything on the net rated LT for those sizes...  they could have quit making them since 15 inch wheels on service vehicles is a thing of the past now...  seems they're all for 16" wheels or bigger...  if you could give me a link or something I'd be very grateful...

[79gmc15]

I have iirc 30x9.5r15 LT on my truck and iirc they are D rated.

[KWKENUF]

With that size tire you might not find the "heavy duty" tire.  But going from a P to a LT,  no matter the 97s or 107s rating will be a huge help. 

Goodyear AT/S has 215/75-15 with a 103s rating.

http://www.tirerack.com/tires/tires.jsp?tireMake=Goodyear&tireModel=Wrangler+AT%2FS&partnum=175SR5WRATS&vehicleSearch=false&fromCompare1=yes

[78 Chevyrado]

best I can find os the BFG t/A in the 235 size has a 107s rating....