Hi CF,
I just put 16" radials on my truck without tubes. My tire guy told me to try it without tubes as he does not like them or recommend them unless the rim won't hold air without em. So far, they have worked great. The ride is super. My old tires were out of round from sitting so long. New tires made all the difference in the world. As far as the size I went with, 215 85 R16 worked out pretty close to the diameter of the old bias ply tires I took off. I know you are working on 15 inchers so I can't help other than to say go close to what I got but in 15.
