Yesterday we hear that a test download of New Super Mario Bros. 2 on the eShop (in the U.S.) resulted in a wait of over 40 minutes. It seems that the first test might have struggled due to that person's internet issues. Here's what IGN had to say about their download.
We just tested a download of New Super Mario Bros. 2 from the eShop - 13 minutes. That's not bad at all.
13 minutes is a lot better than over 40 minutes. As long as you have decent internet, you should be able to grab the game in the better part of 20 minutes.