A maximum RAM limit of 1.5GB doesn't really make sense for a motherboard with only two slots. Many motherboards support up to 512MB per DIMM. So if the limit is 1.5GB, the motherboard would usually have three slots. I haven't heard of any DIMM's coming with 768MB (what the maximum capacity per DIMM would have to be). They might exist, but I don't know about them.

I think that Max Module Capacity is probably the maximum capacity per DIMM, which would place the total memory limit at 3GB.