You don't need a crystal ball to figure out Apple will release a new iPhone handset every year. It's been doing it since the original came out in 2007, and starting with the iPhone 3G, Apple's naming convention has consisted of introducing a new model number every two years, with "s" variants in between. There was the iPhone 3GS in 2009, iPhone 4s in 2011 (the first to use a lowercase "s"), iPhone 5s (and iPhone 5c) in 2013, and now the iPhone 6s/6s Plus.
The one thing that's been true of each "s" upgrade is they've all been faster than their predecessors while retaining the same overall exterior design. That's again true of the iPhone 6s and iPhone 6s Plus, though there's quite a bit more here than a simple speed bump. Apple is keen on saying "the only thing that's changed is everything," and while that's overselling the iPhone 6s and iPhone 6s Plus a bit, labeling this generation a mere incremental upgrade would likewise be selling the devices short...
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips