Yea, if you're shooting 400 iso, at 1/20, you are in low light. Don't expect much speed from any camera in this price range. Again, when I'm in low light, if I can lock in the focus and lock in the exposure, then you get short shutter lag.
Do you realize that you can lock the focus by half pressing the shutter, wait for it to lock, then without releasing the shutter, press the ok button. This switches the camera to manual focus with the current setting. Then, Hold the ok button for a couple of seconds and it locks focus for all subsequent pictures. Then hold the ael button a couple of seconds to lock exposure.
The focus lock may seem cumbersome, but you actually get very fast at doing it after awhile.