I did the same and I'm also sticking with El Capitan. I have no use of Siri, Sierra broke Karabiner (Karabiner Elements mappings are not sufficient for my keyboard), and mouse scroll was also behaving weird on Sierra. f.lux is showing artifacts with fullscreen video. It feels like this will be my last Mac, which sucks because I bought my first Mac three years ago and completely stopped using Windows last year. It might be time to embrace Linux for desktop when it's time to replace the 2015 MacBook Pro.