Depending on the time of day downloads can take longer for any file on any website, You Tube is no different.
After each three minutes, do you see the flashing circle in the screen before it starts again? Yes, then all it's doing is downloading. Traffic may be heavy for that particular file.
You could either wait until the video fully downloads or use a different time of day when it's not too busy. Early morning is usually ok, evenings, then don't expect immediate results.