Hi Maverick,
I'm sure it's frustrating to encounter technical issues on your iPhone. I also own a 4s and I'd probably be very unhappy if it wasn't working properly on iOS 9.
Downgrading to iOS 8 would render the phone vulnerable to hacking, I would not advise to do it even if you could.
We will not be able to help you if you don't describe in which way your iPhone is acting awful. If there are several software issues, you could always backup and restore your iPhone.
Backup : https://support.apple.com/en-us/HT203977
Restore : https://support.apple.com/en-us/HT201252
If you want to tell Apple about your negative experience with the update, I advise you to use their feedback page : http://www.apple.com/feedback/