iPhone 6s and iPhone 6s Plus Preliminary Results
 

At this point the iPhone release cycle is pretty well understood. One year, Apple releases the design refresh that changes the external design significantly while generally focusing on evolving the internal components. The year after, the S variant is released with the same design as the previous year, but with sweeping changes to the internals. This cycle of upgrades allows Apple to focus on updating one half of the iPhone at a time while essentially giving their teams a more comfortable two years to develop their next generation technologies.

http://www.anandtech.com/show/9662/i...minary-results