They're circumaural, so they sit comfortably on the sides of your head rather than mashing your pinnae flat, and their velour pads are nicely breathable; they also mass only a quarter kilogram (260g), and they're an open-back design so that ambient noise is merely reduced rather than totally occluded. (Also, unlike closed-back and especially noise-canceling headphones, they do not produce a constant pressure on your eardrums, which has been suggested to cause hearing loss and certainly plays a role in listening fatigue.) Their reproduction is quite good as well, with a surprisingly flat frequency response for the price range; if that suits you, you're good to go, and if you prefer otherwise, they won't interfere with you EQing your music to your heart's content.
Depending on where you find them, they run anywhere from $100 (Amazon Prime) to $180 (MSRP), so they're considerably less expensive than your QC15s, too. I really can't recommend them favorably enough.
But I will say that Sennheiser is one of my favorite companies. I've purchased 5 different items from them over the past 7 years or so (HD 555, RS 180, MM 550-X, CS 686G, and the GAME ONE headset) and they all still work to this day with fantastic audio quality. I broke the MM 550-X, out of warranty and totally my own fault, and they still replaced them with a brand new set.
Are you saying that the feeling of pressure will stretch the eardrum or something?
I've been told that from an audio standpoint, the only difference between the 558s and the 598s is the bit of foam stuck to the inside of each can on the former. Supposedly removing this foam improves audio quality, although having done this with my home pair but not my work pair, I can't say I have noticed any difference other than perhaps that ambient sound is a little easier to hear without it. I also haven't noticed any difference between my 558s and a pair of 598s I once had the opportunity to try, thanks to a former manager who had a real thing about one-upmanship. So I'm not sure quite what you get for the extra $50 other than style. (Though the 598s are very stylish!)
I've since moved on to other headphones, but I always consider if the headphone is to tight, heavy, or the ear cushions are cheap pleather that makes my head sweat.
The QC20 have been amazing, and have longer than apple's 5 hours battery life. The wireless QC20 will be out soon, and they're rated at 10 hours I think (maybe 8, can't find the article now).
I don't suspect they'll be able to do wireless active noise cancelling, so the argument for the lightning port supporting active noise cancelling functionality is weird... do you want people to go wireless, or not? My first reaction is that that was a poor justification.
i use mine with whitenoise (grey or brown noise, usually) most of the day, and it helps me get in 'the zone' more than anything else.
It was a big discovery for me, as 16 hour days in the lab with studio headphones once resulted in a blocked ear canal, from ear wax melting & reflowing! Weird & gross, I know.