Update 2.1.5 is just a trivial update, fixing some minor bugs. The API documentation has been updated to include the IP address retrieval resource.
YDNS also asks for your help by donating for it. Our promise is to keep YDNS for free forever and we'll keep that promise. However, the development and operation of YDNS is not free for us - we have to invest a decent amount of work and money into it. That way, we kindly ask our users to donate to help us funding the further development and operation of it. Regardless whether you donate or not: YDNS will be free forever.