Brand new iPhone 15 pro aux in car is very bad quality

I just got my iPhone 15 pro 2 weeks ago. My car does not have bluetooth so I have to use aux. when I plug it in to my car and play music it is very bad quality. I plugged the same aux cord into a separate speaker to see if it was the aux and it sounds great through that. My boyfriend plays music through his iPhone 13 in my car and it also sounds great. It has to be something with the phone but I can’t seem to figure it out.