What a hard way to live! I can only guess that your parents remarried after divorce because they found they couldn’t each manage life financially on their own. Or it may be that they support each other is ways that you can’t see. It doesn’t sound like a love match. What they apparently didn’t think about was the impact their arrangement has on you.
Sadly, however much you want to, you can’t change the relationship between your parents. That’s between them. All you can do is love them and tell each of them how their living arrangement makes you feel. Yelling at them or blaming them won’t be helpful. When people are being scolded, they usually get defensive and don’t listen.
Instead, calmly state how you would like your relationship with each of them to change. Do you want more time having fun with your dad? It’s worth an attempt to ask him to do some things with you. Do you want to relieve some of the stress on your mom? At 15, you could take on some of the chores.
You said that “neither of us know what to do”. That suggests to me that your mother would like a change in her marriage as much as you would, but she doesn’t know how to go about it. You can tell her for me that you can’t help her figure it out — but a therapist can. She would benefit from seeing a mental health counselor to get some guidance and support. If there’s a women’s center in your city, she might also find practical help and support there.
You might also benefit from having a counselor to talk to. Your parents’ relationship is not a good model for love or life as a partner. It might be helpful for you to talk to someone who can give you some perspectives about how to choose a good partner and how to build a relationship that is much better than the one your folks have.
I wish you well.