Bluetooth connection issues with new iPhone 15 Pro

My wife and I just ‘upgraded’ to iPhone 15 Pro (big mistake) and have had nothing but bother with it. So frustrating. Took 2 days to get it to pair with Apple Watch, blocked us from our banking apps etc. Anyway the one thing I can’t fix is that it won’t stay connected to my car stereo to play music. Connects for 22 seconds and then the connection drops, it reconnects after around 10 seconds and repeats. Same with my other Bluetooth speakers in the house. I’m up to date with IOS 17.4.1.

All I can find online Re a fix is people with the same issue - and no fix.