Hi..... Sometimes i get earnings like this but some time just 12$ on 15 to 18 clicks but sometimes very high earnings.
15% CTR is an healthy rate for adsense (as I remember and know), more than 20% CTR its risk to be banned by Google Adsense
Yeah, this is good rate. Keep your CTR below 20% to lower your risk to be banned by Google. Else, please follow Adsense TOS for profiting from Adsense for long run.