From my experience both are light, LXDE could be better suited for new win refugees; e17 has some inconsistencies that may scare that kind of users but has more eye candy which make it attractive for someone that has used Linux for some time.
From my point of view, no, e17 is not lighter and I think melodie
's comment is pertinent since Open Box is
I you want a light PCLOS I think the best way is to install the mini versions of LXDE or Open Box and then pick the light apps that better suit your needs, keeping an eye on dependencies.
If you want a beautiful PCLOS install e17. I haven't installed the current version but I think it will need a lot of updates
Edit. I you can, add some memory to that machine it will be much better
I have a desktop maxed out to 512 MB and works fine