Let me tell you what I did, OP.
I thought I wanted the 6+ in the week leading up to preorder. I let my husband talk me into going with the 6, because my hands are small and he thought I'd have a hard time managing it, never mind fitting it into my wee, girl pockets.
I got my 6 on launch day, and it was really nice, but felt so much bigger than my 5s... wow!
Still, it was manageable and I quickly realized that I really wanted a 6+. Soo... I traded my 6 for a 6+. And it felt HUGE.
It was heavy. It made my wrists hurt. Hahahaha.
It's gorgeous, though. This week, my inlaws were in town and we'd planned to hand off 2 of the kids' 5C devices (in flaweless condition with AppleCare+ for another full year) to them because they needed new phones and wanted to try some smartphones without spending a lot of money.
So, my son, who had been wishy washy about what he wanted, finally concluded he wanted a 6+ and we could not find one for him ANYWHERE.
My daughter was waiting for my son to give her my old 5s, because that was all she wanted.
I gave my 6+ to my son and bought another 6.
You know what? The 6 seems small to me now, and I'm looking for another 6+.
My husband just shakes his head at me. LOL. He's got a 6 and he's totally happy.
What the point of my rambling here was:
You get used to whatever you're using. It's amazing how fast the 5s started to feel TINY to me after using the 6 and the 6+, and even more incredible how the 6 feels small to me now after a week and a half of using a 6+.
Yes. You will get used to the 6 if you keep it. My advice? Pick up a 5s again and see if it feels like what you really want compared to that 6 before you take back the 6.
You may be surprised to find that the 5s seems too small.
Or, it may be that you really don't like that larger phone and you'll love the 5s. Still, just something to consider.