A P4 with 1.5 GB of RAM is not so old that you should mess with a lot of super-tiny distros.

If "medium-light" distros aren't performing well, it's probably a graphics chip issue.

What's the output of:
lspci |grep -i vga
Honestly, if this was my machine, I'd quit distro hopping, install a minimal install of Debian/Ubuntu/[insert-general-purpose-distro-here] and just try different desktop environments until one of them pops.