Could the HUGE processing that is required to make a single image.

I am currently doing a city map project and am 'pasting together' the submitted JPG to the publisher from four individual JPEGS. I have the Map Border marked in quarters and then just save as a rectangular JPG the four quadrants and then drop them into a single Photoshop image set to twice the quadrant's JPEG dimensions.

Little more work, but I am not waiting 20 minutes for the computer to process to then 'crash' on me