Is the iPhone 6S as durable as the 5?

I've had an iPhone 5 for 2 years now and I've dropped it countless times on various surfaces from various heights and it's pretty much still perfect.

Is the 6S this durable?

My iPhone 6 plus won't update to IOS 9?

I need hel on how or what I need to do to update my phone it really pissing me off I have been trying for like a week know I go to general and the to software update and it says update requested it does not move from that section

What will happen if I don't pay my termination fee?

So I have an 2 iPhone 6's and an iPhone 5s combined have a total etf of like $1300 and I'm not paying that. I planned to sell the phones to try to pay it off but what if I sell it to an AT&T customer? (Phones came from AT&T) can they just pop their SIM card in and the phone will work since it's locked to att?