15" rallys needed

I have a set of 14" rallys on my 72 Duster now but the 14" just don't do the rear of the car justice, so I would like to find 2 15" rallys for the rear. I thought of going with at lease 7" wide. I My bolt pattern is 5x4 with a 3.75 backspace. I hope the centers from the 14 will fit but I will need the 15" trim rims. Hoping I can find them close to me so freight won't kill me. My postal is T2B1Y5