As with most Wal-mart deals, it's completly YMMV.
SSX 3 is $19.82 at my Wal-Mart.
Metal Arms is $29.82.
Brute Force, Freedom Fighters, and NFS:HP2 are all $19.82.
In fact, the only $15 console games we have other than GBA at my particular Wal-Mart are: Sphinx (X-Box), and Harry Potter and the Sorcerer's Stone (PS2).
Could be the fact that the deal was spotted over a month ago.