The page figures are only going to be cumulative if you print in a pure monotone, ie 100% Cyan, 100% Yellow & 100% magenta. This is a virtual impossablity and the printer is going to be blending the print colour from all available cartridges. So the 1500 pages at 5% is an average figure for all cartridges on a set colour sample print. Clearly the life of each cartridge will be affected by the colour balance of what you are printing. So 2000 pages is actually pretty good.