Yep, iOS 9 is another terrible release from Apple. I have a similar issue where my phone messages won't delete. I delete them and they keep popping back. The UI is also laggy on my iPhone 6 Plus, and some apps won't let me update from the app store -- tells me I can "open" the app, but not update it.
Syncing through iTunes 12.3 has never been worse too. It converts all my phones (26,000) to "other data," and half the time the sync stalls. iTunes has been like this for awhile, so it's nothing really new, but 12.3 made it even slower.