The palm's a bit faster than an old 11/780. (Which is more than 25 years old now) It's also possible that the Lisp you're using considers the entire memory part of its root set, which can slow things down a lot, as can poor structure allocation policies. (Parrot's dodged both those issues)

It may also just be that the GC on that version of lisp sucks, and the folks writing it are used to long pauses while running. :)