Congratulations on your new phone. Yes, I think it should last you quite a while. After a couple years, it might be noticeably slower than the then current phones, but it should still work. Right now it's one of the fastest iOS devices ever, only iPad air 2 is slightly faster. Plus, the improvements in phone speeds may start to slow down as we have very mature products at this time.
You made a good choice as the fastest iPhone now will have the best chance to serve you longer. Enjoy your iPhone 6 and let us know what you think.
Really? Ive had my 5S since October 2013 and a little over a year later I am thinking of buying a new phone because its battery has completely gone to s#hit. Honestly, a phone with a premium price tag should last you longer than a year... I now am dependent on having a power source close to me cause my phone wont last more than 7 hours.