My 2012 S-line was on steel springs, my 2015 Avant is on air suspension. If you have the opportunity try air suspension, for me it is far better. Also the 2012 did not have a powered tailgate, the 2015 one has. Not sure when the change over came in. Parking sensors are standard.The rear view camera was a relatively expensive option in 2015, from memory ~£1K.
I prefer the S-line sports seats over the standard SE version, but we are all built differently!
Standard music is good enough, Bose is very slightly better if you can get it.
Not much else I can offer really. My 2015 Avant is a Biturbo, now that is definitely worth having!