Either it's an issue with your internet connection (too slow, or too far away from the wifi source), or an unsurprising server lag. After all, this is a worldwide release, and a bunch of countries have it available in the eshop now. There's going to be stress on Nintendo's eshop servers from everyone trying to download a, iirc, 1.7 Gb game. Particularly one that is called Pokemon, sells millions every gen, and sold out all preorders in Japan. =p
So you may need some patience, I suppose. If you have any other questions use the Q&A thread sticky next time, please. Closed.