jolla gives us only less sounds..
so if you have a folder with your personal ringtones you can do this from terminal:
cp -r /home/nemo/YourRingtones/*.mp3 /usr/share/sounds/jolla-ringtones/stereo/

where *.mp3 is all mp3 files you have in YourRingtones folder!
Then you have now a list of sounds more large !