Compared to the steelbook for the first movie, which was available for under £10 for a long time, I guess £15.99 still feels a little bit high. But with the 10% discount, having it shipped to the US is cheaper than from Amazon UK.
I don't understand the Zavvi shipping. I think it used to be just one really low price (.99?), sometimes even for multiple items in one order. Then they raised the price, and now there's that discount, which usually takes .99 off for me. But it looks like each item now ships to the US for £2? I don't know, it's very unclear to me.