Note there is a useful a lens modification guide for the Acer X1240 at
http://imgur.com/a/FOgXW The Acer 6150 and presumably the 1500 are very similar. The specific steps for the 6150 lens modifications include:
Once the lens is off and the zoom adjustment screws out. Pull the zoom adjustment ring off.
Remove the 3 zoom stops and push the lens assembly in fully from the rear to zoom down as much as possible. Note it can drift back but this can be fixed with a fine screwdriver after reassembly.
To enable recentering of the lens, dremel the black plastic mounting screw holes in the lens assembly so the lens can sit about 2.5mm lower.
It is worth masking off the rest of the lens to protect against dirt.
Add spacer nuts and washers to offset the lens by 5.3mm and enable focus at 28um xy. Probably less than this is needed for 35-50um xy resolution.
Reconnect the lens assembly and slide it down to close to level with the bottom of the plastic projector housing. I've found you also need to move it slightly away from the fan. Tighten and test the projector to see if the lens focus is centered ok vertically and right left. This may take a couple of iterations.
The projector will then need to be realigned with the build plate. This will probably involve more spacers to elevate it.
Refocus.