If you're trying to burn an ordinary audio cd then 15 songs sounds about right. A 700 MB disk will hold a max of about 79 mins & 54 secs. So 15 songs divided into 79 mins is about 5 mins each right?!

If you want to burn an mp3 disk then you need an mp3 player than can play mp3 cd's for normal cd size. Or play it in your set-top dvd player or your computer. Yes an mp3 disk can hold perhaps 4-8 times as many songs depending upon the bit-rate they were converted to & their files size.