Maybe a bad idea. The nearest radial size is 225/75R15. IMHO, fatter tires are a bad idea, but slightly taller tires are OK. You definitely do not want shorter tires.
I've got 15" Carlisles from Discount Tire on my Sovereign
and have 6000 miles on them (one round trip to Seattle). But my latest tire deal (for the '77 Safari) is new wheels and Maxis 225/75R15s tires from Discount. One of the premier Airstream restorers, UWE
, recommended Maxis.
If you need wheels, you might think about 16" wheels, which allows you to go to LT tires and only add about 1/2" to the standing height of the Airstream. However, I don't think bigger wheels/tires add any margin for a Safari. I calculated the max load bearing on any individual wheel, even with a 30% uneven distribution, and I came up with 1550 lbs. A 15" load D tire at 65 psi can support 2200+ lbs. That's a lot of margin.
Now all you have to do is decide whether ST (special trailer) or LT (light truck) tires are fundamentally more reliable. You have the luxury of two axles, so a tire failure biggest issue is usually skin or wheel well damage, not loss of Airstream.