You can always go for 6S. To be honest with you, I ordered the 6S+ till I read about this. I'm picky about my gadgets like majority of you. Curse OCD!!!

And I thought back when I had 6+ for few months before I sold it. I remembered how inconvenient it was to carry the big thing in my pocket. And how the apps used to be pretty stretched out. While my wife's regular 6 was a pretty comfortable size to carry and to use. For last few months, I have been using an ancient iPhone 4. I admit that it is actually nice to have a tiny thing around and not worry about feeling a thing. So, due to this 6S+ issue, I decided to cancel my order and placed the order for 6S instead.
As many have said, each to their own. So, if you don't want your OCD to go off all the time and lose sleep over this issue. Exchange for the 6S and sleep happy.
Just my 2 cents.