Difference between AICS 1.0 and 1.5?

No cheekpiece would be the obvious. It might lack the bipod spigot - not sure when they began adding those to the chassis. Early AE rifles have a welded chassis, which quickly switched to pinned and pressed, so it's possible that a 1.0 AICS might show those characteristics as well (not sure when they swapped over, and if it pre-dated the AICS release).
 
As mentioned, 1.0 has no adjustable cheekpiece and no bipod spigot. I converted a AE with a 1.0 and a AICS 1.0 chassis to 1.5s with little work

before
Picture774_edited.jpg


you can see the 1.0 chassis has provisions for the cheekpiece posts from the factory
Picture834.jpg


purchase cheekpiece and hardware, modify skins
Picture833.jpg


after
Picture831.jpg