I don't think 15 years difference is a big deal. I met my husband when I was 26. He is 13 years older than me.

I feel bad if your parents threaten to cut you off if you stay dating him. I see that as extreme. But I imagine they do see you as vulnerable and worry about that. I'm thinking that they don't want to support you financially possibly living with him in the future. They likely don't want that to equal partially supporting him financially. If you ever get very serious about him I think you should be able to support yourself, financially, 100%, and if you do, keep your expenditures for just you, and not partially for him, too. Separate accounts and 50-50. Believe me!