People who think that 'casual/hardcore' is about types of activities and/or skill are completely clueless.
You raid 6/7 5 hours per night and are sitting at 8 heroics? You're a hardcore player. A scrub, but a hardcore player.
You raid 2/7 4 hours per night and are sitting at 14 heroics since winter? You're a casual player. A good, yet casual player.
You do pet battles, archaelogy and level characters 5 hours a day? You're a hardcore player.
You play 1 hour per day while sitting on a gladiator-level pvp rating and 14/14 heroics? You're a casual player.
That's how it is, deal with it.
15 hours per week is quite casual.
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In case you haven't heard, you can extend raid IDs. And yes, I know a lot of (and a part of) such guilds.