I've owned every iPhone since the first one, and are a happy user of the iPhone 6. But I'm not sure I will buy next years iPhone 6s. If Apple keeps following the way they update the iPhone that is, and just do a small hardware upgrade and everything else is the same, and they call it the 6s. As they usually do.
The reason is that I'm very happy with the iPhone 6, I have absolutely nothing to complain about. There is nothing I want to change with it. And to me the iPad is way more important, because it's my main computer. So it's more likely that I will upgrade the iPad instead. Either to the Air 3 or the rumored iPad Pro. I'm very very happy with the iPad Air 2 though so if I would like to buy a new iPad Air next year, then it need to have something really cool that makes it necessary for me to upgrade. And I don't think the Air 3 will have that but I'm sure the rumored iPad Pro will.
But it's a completely different thing if Apple releases an iPhone 7 that is once again a completely new iPhone. Then I'll of course will upgrade my iPhone again.
The most likely release date for the iPhone 6S is September 2015, which would follow Apple's iPhone release schedule history. The iPhone 6 and 6 Plus were released in September 2014, the iPhone 5S and iPhone 5C in September 2013, the iPhone 5 in September 2012 and the iPhone 4S in October 2011.