Kodawarisan disassembled one of the new 15" PowerBooks, and posted an extensive collection of photos from the diassembly.
They were able to identify the PowerPC G4 used in the 15" PowerBook, and it is reported to be labeled as a 7447.
Apple Documentation had implied that the processor was a 7457. The only functional difference between the 7447 and 7457 is that the 7457 is capable of supporting an L3 cache.