The interwebz says:
http://www.bandwidthplace.com/what-are-the-bandwidth-specifications-for-pandora-spotify-itunes-radio-and-beats-music-article/Pandora and Spotify
One hour is about 72 MB of bandwidth usage (15 hours would then equal out to 2 GB). On mobile, if you use a sizable bandwidth cap, you should be able to easily use a 64 Kbps HE-AAC–encoded stream setting. For both mobile and desktop, make sure you’re getting at least 1–2 Mbps download speeds on your device. Use an Internet speed test to determine this.
iTunes Radio
One song is about 4–11 MB, so with a 1 GB data cap, you will get approximately between 100 and 256 songs per 1 GB. On mobile, you will want to use a higher stream setting for iTunes Radio. Also, for both mobile and desktop, make sure you’re getting at least 1–2 Mbps download speeds
Beats Music
Whoa! Supposedly there are no data charges, but then you’re paying $14.99 a month anyway — on top of your data usage — and you have to be on an AT&T phone plan. Beats Music is also super-high-quality audio, so you will want to stream at the highest setting. Plus, you need to make sure you have better than adequate bandwidth speeds running. More like 5 Mbps download, for sure. You’re paying for this, so you better make sure your streaming is at the next level.