I swatched the colors in Urban Decay 15th next to Naked and Book of Shadows 2 and 3. I don't have every color from the Book of Shadows after my depotting adventures though.
Let's start with the lighter shades:
Midnight Rodeo is close to Sidecar, but Sidecar has less glitter fallout. Midnight Rodeo is a bit deeper and more neutral than Sidecar.
Midnight 15 is very shimmery and shiny next to Virgin. It is also more silver. Midnight 15 is lighter than Sin.
Flow is peachier and lighter than Sin.
Chase is less warm and gold than Half Baked. It is more bronze than Toasted.
Deep End is more turquoise and less blue than Haight.
Half Truth is more blackened and less warm than Psychedelic Sister. It is deeper than AC/DC.
Deeper is more of a neutral brown compared to the warm bronze Smog.
Ace is deeper and less shimmery than Gunmetal.
MIA is a bit lighter and warmer than Darkhorse. It is deeper and more pigmented than Twice Baked.
Blackout is deeper and completely matte compared to Perversion. It is deeper than Creep and lacks the micro shimmer.