I own a 600d and save all the files locally on the Pi.
17 seconds is my time too, but i dither although. We are limited to a USB2 Port while using such an old camera.
A friend of mine did a test with an usb3 camera (some Sony) and it was faster (3-5 seconds).
I'm okay with that time. I do 300 seconds exposures and dithering. That are 11 pictures per hour. And i don't need to take dark frames... take that in count for the whole session.