Error type: "Forbidden". Error message: "The request cannot be completed because you have exceeded your quota." Domain: "youtube.quota". Reason: "quotaExceeded".

Did you added your own Google API key? Look at the help.

Check in YouTube if the id PLx15eYqzJifcp4_UJ12_OIhnk5nmbnm2f belongs to a playlist. Check the FAQ of the plugin or send error messages to support.