15x25 feet?? haha.... er..yeah good luck..
we have shit loads of normal size ones at work.. but 15 x 25 feet.. that is a billboard.
you cant get those as one sheet ..they are lots of sheet postered up together to form one big image.....
best of getting an image off google images or a website. then saving it to disk take it to a printers, Prontaprint Alphagraphics etc and they will print you a large format copy for a few quid....
yah but it will be low res and look shit