Jeremy Horwitz, writing for 9to5mac:

Transferring files from your old iPhone to a new iPhone 6s or iPhone 6s Plus isn’t difficult, but after a reader emailed about the many, many hours he expected to wait for the old-to-new iPhone transfer process to complete, I realized that his experience has become more common — even though it’s not necessary. Years ago, iTunes was the only (and fairly straightforward) way to transfer one iPhone’s contents to another. But now, between iCloud, larger device capacity sizes, and iTunes encryption options, there are certainly ways to turn a simple process into a day-long ordeal.

This quick How-To guide is designed to save you a wasted day by helping you select the best options in iTunes and get most of the work done ahead of time. I’ve used this process more times than I can count, and beyond working perfectly each time, it requires far fewer hours than relying on iCloud…

As far as I can tell, this advice extends to all new iOS devices. Tuck this one away til your new device gets here.