The thing is: Each and every digital product suffers from piracy. This simply needs to be covered by your expected earnings.
Simple as it is.
Furthermore, you can not just count the number of downloads and claim all of these would have been buying decisions.
When it is available for free, people will get it. Sometimes they even don’t use it.
Some of these guys are even just collectors.
Lots of them can not effort your addons as they live in countries like Iran or Egypt.
So no need to be sad about not earning 15k Euro. This is simply not true.
It is most probably more about 1000 Euro minus simmarket fees minus tax.