iPhone 6 Plus iOS 8.4 Problems
Although my iPhone 6 Plus iOS 8.4 battery life is great there are some complaints about iOS 8.4 battery life overall. There are also an array of other issues and iOS 8.4 bugs that can cause frustration for owners.
Apple Music and in-car entertainment systems don't work well with the Up Next feature, but the app still works overall. Siri is not functioning in my car any long as it tries to use the Lightning connection instead of Bluetooth.
You may not run into any iOS 8.4 problems on your iPhone 6 Plus, but it is a good idea to double-check the Apple Support forums for potential issues and ask friends who already upgraded and use the same apps or accessories.