The lower on an AR-15 just holds everything together and takes very little stress.
Generally true, with a couple exceptions.
Magazine well takes some oddball force vectors, none very extreme, but still significant. If you do a NURBS study of the magwell, the highest forces, though, are around the latch.
The takedown pins and trigger pin do not have a lot of force, but they do have tight dimensional tolerances.
The biggie is the recoil tube support. There are a lot of forces that knot up right in that small area. This is the location where most polymer lower fail at some point, as you both need a lot of material strenght there, and you want to not have a lot of volume, or you spoil the grip geometry.
Above, a good idea was put forward--use a metal (stainless steel might be ideal) insert to support the mag well, and the through pins, and the buffer tube support, then laminate all that into a wooden blank. Use a catalyzed acrylic resin (stronger than the phenols) and the wood would largely be for show.
But, you could use some spiffy stuff--mescquite, zebrawood, flame maple--which would be cooler than all get out. (Just not light [
])