I am developing my game for the iPhone. So I am using an orthographic size of 5 and a PPU of 64 for all my images. I designed my images in Illustrator, so I reduced them to a third so they'll fit the right dimensions on the device. Because of that some of my images are quite small, some are as small as 15x15px. These small images are already pixelated before I place them in the project. How can I workaround or determine a better PPU and orthogonal size so that I don't need images to be as small as 15x15px?