To put it bluntly, you probably haven’t seen your dad because he hasn’t tried to see you. There’s a good chance that he has a new wife as well as a new family and he may or may not be interested in seeing you. Don’t take it personal as that’s how some men deal with the breakup of their family. It may have nothing to do with you other than how he dealt with leaving
Regardless of why you’ve not seen him over the last 15 years, your mom’s feeling are going to be hurt when you first ask as she’s worked hard as a single mom to give you a decent life and trying to be both mother and father to you. She’s either going to cry a lot or scream a lot and say things she won’t really mean out of that hurt
Since you are 17, is it possible that you can wait another year to meet him? By then you’ll be an adult and you won’t need her permission to see him and he won’t feel obligated to offer to take you in. Assuming that you have some other family members like grandparents, aunts, uncles, etc, maybe they can fill in some of the blanks of where he is, so you can do your own search to locate him. Just don’t show up at his front door and say surprise dad and expect a welcoming hug, Send a letter or make a phone call to reintroduce yourself to give him time to decide how he feels about you showing back up in his life and possibly disrupting his calm or not so calm life. Don’t assume that he’s sitting there waiting on you to show up at his door and be ready to accept whatever or however he reacts. Keep it more as I just want to meet the dad I’ve not really known and would like to see what I’ve missed. This might not turn out like the movies lead you to believe and it may or may not turn out with a fairy tale ending.
Whatever you decide to do, good luck