Taking a photo out of iphoto and into photoshop?

When I take a photo out of iphoto on to my desk top & then put it into photoshop the file size gets huge is there any way I can import to photoshop and keep the 15x10cms size - I have bridge but dont really know how to use it any help would be great thanks as I am doing part of a quilt for charity and need to learn tit for this purpose