If the bean mix has red kidney beans, I would probably soak first. It helps break down a substance in the beans that can be a mild toxin. They still have to be cooked well, but soaking helps ensure it cooks out.
If you absolutely can't soak, I would probably do 45 mins with 15 mins of natural pressure release. You're probably going to have some beans that are overdone that way, but it's better than risking having the red beans undercooked.