Jay Leonhart, who has played bass with just about everyone, provides the pulse and creative solos. Guitarist Peter Bernstein shines with sparkling runs and Monk-like chords. Tom Aalfs reminds us that the violin sings and, with its tone, is one of the best instruments for "singing the blues". (Incidentally, about all I can find out about Aalfs is that he stands 6'5" and hails from Massachusetts! With his ability we should hear a lot more about him.)
Monk's music isn't all joy. His darker side is shown by "Misterioso" and "Round Midnight". On the melancholy blues, "Misterioso", the familiar opening and closing theme alternates between guitar and violin and is alluded to in the intervening guitar ad lib. On "Round Midnight" Aalfs shows why sometimes simply melody with feeling is the right way to go.
Bassist Harvie S once said "Play the music, not just the notes." That is what Group 15 is all about.
P.S. For the curious: "Fifteen" refers to fifteen strings, not a section but electric violin (5), guitar(6) and bass (4).