Simple trophy, you need to upload 15 DIFFERENT songs to your Vita through the file management section in options then onto this game.
By the time i got around to doing this Trophy, i was semi good at this game so i uploaded 15 songs that i thought would be cool to smack around some enemies in. You could hypothetically upload 15 songs that go for 30 second each to quickly earn this Trophy. Whatever works easier for you, though i found it more fun to do proper songs.
One thing to note, is don't expect the songs to have matching beats. I tried to get some of the songs to match up according to the in game tracker which calculates beats for you and let's say ... it didn't work very well
but hey, at least they tried right?