There are "trailer rims" that are split and 15", 6 lug on 5 1/2.
I have some. They have the hub cap clips.

I have never seen a 15" split 8 lug, yet.

By split, you mean two piece with a ring, and by 8 lug you mean 8 lugs? smile

A 15" tire only fits a 15" rim.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn