Stating the obvious, but you plug in your phone and in iTunes you clicked update/restore depending on what you are trying to do, and let if fully download right? Once it installs on your device, it moves itself to the trash.
Here is what happened
1. Plugged in my new 6S
2. iTunes prompts me for an update
3. I select "download and update"
4. iTunes starts downloading 9.2
5. iPhone gets stuck on a "slide to upgrade" glitch (download still has not completed)
6. Unplug the iPhone and do a restart
7.plug the iPhone back in
8. Now, iTunes prompts me again for an update
9. And now step 2 thru 7 are in a constant loop
The 9.2 update takes 2 hours to download and I think the iPhone timesout.