Pentium M 1.5Ghz is slow for browsing, period. Debian is just about the finest distribution for older hardware, in my opinion. (If you are not already using a "lightweight" UI such as Xfce, Fluxbox, LXDE, etc then give that a try to squeeze a little more "oomph" out of your antiquated hardware.)
For best results I recommend browser add-ons such as: adblock plus, noscript, flash block, etc.
Blocking all the flash animations and scripts should hopefully speed up your perceived browsing experience, good luck!