I consider 1500 g as being light for a 26 mtb disc wheelset for XC riding. I know there are much lighter wheels, sub 1200 g but these are limit rider wieght - let's say the rider is 100 kg max.

What would be a breakdown of the parts:
f hub, r hub, spokes (32 h hub), nipples and rims.

Would it be possible to build a sub 1500 g wheel set using the hubs below (F/R 159/241g ) ... that looks stunning.

You should be able to build a sub 1500g wheel with those hubs without much trouble. Something like a Crest rim, Sapim cx ray spokes and alloy nipples should be about 1450-1500g. Should also be pretty strong.