Had some progress on this issue. I use the cable that came with the phone and a type C to type A adapter (from Amazon) once it stops working, restarting the phone solves the problem but it doesn’t last long. It turns out, on my VW head unit, there is an option to “safely remove usb” similar to disconnecting a flash drive from your MacBook. If I do this, I have no problems.
In conclusion, you need to either find and use the “safely remove usb” option every time you disconnect or restart your iPhone 15 if it won’t connect.
Not an ideal solution, and not one I have ever needed to use before, but it’s all I’ve got for now.
Hopefully, Apple will sort out iOS soon so it will work like my 11pro did for years.