15 x 1920 x 1080 x 4 = 124416000 bytes = 124416 kilobytes = 124.4 Megabytes
and that is if they aren't transfered to a 2x2 ratio in which case it would be:
15 x 2048 x 2048 x 4 = 251.7 Megabytes
It might be a bit much loading them all at the same time.
Try putting them in a layout that isn't loaded in it's entirety or find a way to reduce the image size, would be my advice.