Transfering photos and videos between your iPhone, iPad and computer with Simple Transfer is extremely fast. If you experience slower transfer speed, please try the followings:
If you still have this issue, please try using USB transfer with the Desktop app. It usually doesn't have any network issues and is much faster than WiFi.
USB transfer is exactly the same as WiFi but you connect your iPhone to computer via USB cable. Then you should be able to see the device name on the Desktop app (it will show USB instead of WiFi under device name).