My iPad mini has been amazing since day one. Fast and plays 90% of all games in App Store and awesome battery life. I upgraded to iOS 9 and the minute I switched my iPad runs at laggy speeds and battery life dropped. Unfortunetly I made the decision to wipe everything to restart from scratch and it did not help . Now I have none of my data and my iPad is not worth searching the Internet. I have the highest speed internet that you can possibly buy and iOS 9 literally killed my iPad from the first second.
Thanks for the warning. Like you, my mini 1 still runs like a dream and there's very few games that I have wanted but can't due to not having latest ios. I'd love to upgrade but can't afford to yet, so this one will have to do me for a while yet.
Try hooking your iPad on to your PC or MAC, doing a backup and then a restore from iTunes, during which you opt to keep your data and settings and it'll do wonders for your device. Many devices tend to be laggy after major OTA updates as there is junk left over from the previous iOS and Apps. A restore performs a clean install on your device. Just don't forget to back up your data and your apps before doing a restore. Hope that helps