Although the holidays are over, the Holiday Party Pack (or Christmas Party Pack) is still available. Not for much longer though, as the pack will be taken off the shelves as of 15 January, according to the official site. That means there's one week left to buy the pack. Although likely, the US Holiday Edition is not mentioned as going out of sale next week. The price of $15 hasn't changed.

[Update 14 January, 13:50] The pack will be available a little longer even, until 24 January. So if you still want to get it, you have a little more time to do so.