i have always been a user of the iphones but saw the galaxy s6 and just had to try it out. Well two months in and I miss my iPhone! and thinking about switching back. How many people have switched to the galaxy from the iPhone and now switching back?
I know this won't be the popular answer, but I say get what you like. The 6S is probably 3 months away and that's a long time to be with something you're not happy with.
You'll be out some money, but sometimes you just have to scratch that itch you know? I did the exact same thing with the LG G3 last year. Bought it in July, sold it on eBay in August, went right back to my trusty 5S and never looked back. It was a GREAT phone, just not for me.
In my experience with Samsung Galaxy S phones (I tried an S4 for two days and my niece has an S5),the user experience only gets worse with touchwiz. It's like it has a shelf life or something and starts to rot the longer you use it. If you're unhappy with it after two months, by September you'll be ready to stab it with a butter knife.
Get what you want...life's too short!