It's a decent term and although being a .net.au brings down the value a lot, as Martin said at least the term fits with the extension (given .net.au is used quite a bit in the ICT space).
I think $15k is very high though. I don't think you could get anything close to that, just look at some comparables that are arguably some of the best terms you could have:
poker.net.au $5k
melbourne.net.au $7.5k
sydney.net.au $8k
creditcard.net.au $18k
creditcards.net.au $22k
I think if you find the right buyer you might get low-mid four figures (best case scenario). I think it's highly unlikely you would get five figures for this, but for your sake I hope I'm proved wrong!