I'm have a struggle downloading updates on iOS 9.0. They often stall, sometimes it appears I may have multiple downloads for the same app or update, which consume lots of free space.
The circle progress meter goes between two values repeatedly. If I cancel one by hitting it to stop, then I get one going forward and not two. Rebooting doesn't fix it.
I did fix it by shutting off auto updates and shutting off wifi (it was. 300+ MB Microsoft Word update) and eventually cancelled it after that. Then I removed it and redo loaded it from scratch.
I've had this issue on my iPhone 5S and my iPad 3. I'll likely file a bug.