Most 15" have a lot of back space. From 3.75-4.
Anytime you add more side wall it will have less side wall stability.
For the cost of buying alloy 15"s unless they are a screaming deal, you have far less tire to choose from in 15" though they are much less to buy per tire.
I have a set of steal email@example.com on 35x12.5. With the lower psi needed to get good wear about 27psi it can be a handful in high winds with the lift. With a 2d. I paid 42$ for a rim very cheep. tires were 225. works with even larger tierods. more an off road set up then good street.