Q: iPad mini os upgrade

My old iPad 2 is running iOS9 just fine, so if a 5 year old iPad can run it, your mini should be fine.

Ideally, your iDevice should maintain a minimum free storage amount of 4- 6 GBs or greater on any iDevice (the more free space, the better) , plus, more than 50%-60% battery status to ensure proper operation, as well as, to ensure the possibility of a successful iOS upgrade/update installation.
In addition it is best to upgrade an iDevice connected up to a computer running iTunes with you iDevice sync'd and backed up through iTunes rather than Over The Air (OTA) using a wireless WiFi connection, if this is possible.

Doing a major or critical OS upgrade/update can be risky to do over Wifi or cellular due to the potential of data interruption or data drop outs causing issues with the download of the OS data and the subsequent install to the device.

If you have no other choice than to use Wifi, then make sure you have a strong and stable connection signal the will not induce the potential for data drop outs.

I prefer the iTunes method as there is minimal risk and I have never had ANY issues with ANY OS updates using this method.

Good Luck!

fI agree with Michael's suggestion to always update via iTunes.

Here's my opinion on it. The iTunes method downloads the whole iOS, which will be over a gig. The Over the Air method download is much smaller, so it's kind of like installing just the patches or the parts that update your software. I much prefer the totality of a clean install. Not to mention if you use iTunes and backup before you install it you will have a fresh install to restore your device from in case something goes wrong.