It may be difficult to understand quickly-spoken Japanese if you haven’t practiced doing so. However, there just so happens to be a show in which the characters talk especially quickly. That show is オー！マイキー. As a plus, they mostly talk about things which don’t require much vocabulary to understand. It might be good for listening comprehension. It’s also just a funny show.
Example of some scenes from it: (of the twins, the ones who talk the fastest.)