One of the changes includes the introduction of mini games on the PS3, a small attempt by Sony to support casual gaming. These mini games were previously only available on mobile devices like the PSPgo. Anyone who already owns mini games will be able to transfer them to their PS3 via the instructions Sony has posted on the PlayStation blog.
In addition to the mini games, v3.15 brings the ability to transfer data between two PS3s via Ethernet. The update is small, but demonstrates Sony's continued efforts to improve the PS3 as a platform. While they still face some PR issues, Sony is competing well with Microsoft these days.