basically you need first a script or code which will read the contents of your folder which have the images in question in.
These then need to be held in an array.
Then creating what would be a template page, designed to hold 15 images, using the array as source, but this way keeping everything dynamic, now by using something like the url, you can pass a value across, every time you click say the NEXT link, it adds a value of 15 to the floating number, this floating number is then whats used as a starting point in the array and the following 15images after this number are loaded, and so on.
The NEXT link would also be Dynamicaly set aswell by using the floating number.