Your issue appears to be different than what is experienced in this thread. For example, before my issue was corrected, I was able to get Siri to accept my commands and would be fine with Internet searches. As soon as the function required interface with another app is where we ran into trouble. For example, I could have Siri understand that I wanted to play "Pink Floyd", but it would try but not succeed engaging Apple Music for that purpose.
To to downgrade you need a computer with iTunes and your phone connected to it. You need to find a reputable site that link to Apple servers that maintain the ipsw files for iOS 9.1 for your specific phone. You then need to download that file to your computer. Connect your phone to your computer and back up your phone. Once you have done that click [option] Restore in iTunes on your phone tab. That opens the finder and locate the downloaded ipsw file. On a pc, I think it's [shift] Restore. I would then set up the phone as a new phone while in 9.1 but don't activate Siri. Once that is set up, got to settings and update the software to 9.2. Once that is done then you can connect to iTunes where it will give you an option to restore your back up. Good luck.