I'm not sure if the 15 and 16 have been discontinued but I know there has been quite a bit of confusion with them. When they first came out the 12 channel antenna was not WAAS capable and software package was different. Some packages are still being sold that way. I just bought The 18C for my bow and the 18c with gps for my console. From what I understand the Gps can be linked to my bow also. The 15 and 18 models have 320 by 240 resolution and the 16,19 and 104 have 640 by 480. Those three were out of my spending bracket