if it's not the displacement map thing, i would guess that one of your lights has an image attached to it, to cast shadows of a pattern, i think i remember a RDNA light set that had bats attached to a light set, so maybe you've got something like that, check your lights in the material room to see if there is an image attached to one of them.

AS for your memory issues, make sure you have at least the Sr2 update, then what i always do is slide the auto bar to the top, then click "Manual settings" and just uncheck "texture filtering" i manage to render just about anything like that, usually a 3000px + no problem.

anyway hope you fix it as that looks like a nice character under dem spots.