Re: customize-apropos-options takes forever...

[Richard Stallman]

        Would you like to try running Emacs 22 under a debugger
        and stopping it a few times uring this operation?
        If you notice a place that shows up frequently in the backtrace,
        that might be the place that is using the time.

    I feel comfortable with the lisp debugger, but not with gdb etc.

You can try using debug-on-quit and the Lisp debugger.  If the
slowness is at Lisp level, you would find it that way.  But I would
guess it is at the C level.  If so, you could only see it with a
C level debugger.