If the figure is dilated by 1/2 it will become smaller because 1/2 is less than 1. To find the dilated side lengths, multiply the original lengths by the scale factor. The length is 15 * 1/2 or 7.5 cm and the width is 8 * 1/2 or 4 cm. The new image will be 1/2 the size of the original image.
Hope this helps!