What's the Name of That Book??? discussion

I read a paperback about mid-70's. It had a title that was basically a year number, 2055, 2255? I seem to remember a "55" but I couldn't find anything with that clue. It remember thinking it was sci-fi, but I'm not sure if that was how it was classified as. The story featured a male protagonist who investigates? Invited to join? a group of people that were separate from "normal" society. The group has created a Utopian society in which members learn to transcend (?) or control their body functions with mind. I think some sort of astral projection was involved? The protagonist tries to become a member. Part of his training is to see normal society as the activity of brutish animals. He learns to pity them and I think maybe forgiveness is part of it. I seem to recall he gets kidnapped and tortured by normals but due to his new outlook, is able to rise above any pain or harsh feelings. He may or may not have been killed in which his mind transcends and leaves his body. I didn't understand a lot of it when I read it (low teens). But parts of it stayed with me (obviously). I'd be morbidly curious to read it again now that several decades have passed.

I figured that was probably a trash novel of the day and would be unlikely to find. But I'll bump once before letting it rot.

2150 A.D. maybe?

That's It!! Thanks!