By default, Fedora 15 does not includes support to play multimedia files such as MP3. You will need to install additional package in order to play MP3 on Fedora 15. But don't worry. Its not difficult to enable MP3 support to Fedora 15. Do the following task if you want to play MP3 on Fedora 15.

Step 1. Check if your system already registered with rpmfusion repository.
Type this command on Terminal to check

ls /etc/yum.repos.d/ | grep rpmfusion

If it return nothing, then you must install rpmfiusion onto your system. Do the following step.

su -c 'yum localinstall --nogpgcheck http://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-stable.noarch.rpm http://download1.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-stable.noarch.rpm'

Then install  gstreamer-plugins-bad gstreamer-ffmpeg using command

sudo yum install gstreamer-plugins-bad gstreamer-ffmpeg -y

That's it. Now you can play your favorite music right away.