And, to expand on etc76's point, in Audacity you have the option to change the bitrate when creating MP3 files. I believe the default in Audacity is 128kbps but since the LiveATC archive files (the source for just about all clips here) are only 16kbps, using a higher bitrate in Audacity only results in a larger file without any improvement in sound quality.
Drop the bitrate to 16kbps in Audacity and you can get a 10 minute clip file under a megabyte in size with no degradation in sound quality.