If you create some symbolic links you can avoid the need to update the configuration file when you install a new edition of TeX Live.
As the user who manages your TeX installation (probably this means root or sudo):
cd /usr/local/texlive
ln -s 2015 current.2015
ln -s current.2015 current
The configuration file 09-texlive-fonts.conf should be created in /etc/fonts/conf.avail with a symbolic link from /etc/fonts/conf.d. So, as root or with sudo, create /etc/fonts/conf.avail/09-texlive-fonts.conf with the following content:
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
<dir>/usr/local/texlive/current/texmf-dist/fonts/opentype</dir>
<dir>/usr/local/texlive/current/texmf-dist/fonts/truetype</dir>
<dir>/usr/local/texlive/current/texmf-dist/fonts/type1</dir>
</fontconfig>
If you also want to make available fonts from TEXMFLOCAL:
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
<dir>/usr/local/texlive/current/texmf-dist/fonts/opentype</dir>
<dir>/usr/local/texlive/current/texmf-dist/fonts/truetype</dir>
<dir>/usr/local/texlive/current/texmf-dist/fonts/type1</dir>
<dir>/usr/local/texlive/texmf-local/fonts/opentype</dir>
<dir>/usr/local/texlive/texmf-local/fonts/truetype</dir>
<dir>/usr/local/texlive/texmf-local/fonts/type1</dir>
</fontconfig>
Then as root or with sudo:
cd /etc/fonts/conf.d
ln -s ../conf.avail/09-texlive-fonts.conf
fc-cache -s
If you update TeX Live or install a new version, you can simply adjust the symbolic links and run fc-cache -fs. In fact, in many cases, the cache will get updated relatively quickly even if you don't run fc-cache because you will get some font package or other updated by your distro package manager when you update the system.
Do note that for some applications you would also need to run mkfontscale and mkfontdir.