All you're doing in the first vid is a lazy 80% serve and falling off to your left.
If you want to add the last 15 mph, you need to end up, after hitting the serve, about 18" - 3' inside NML.
Like throw a ball. If you stand in place, you cannot throw far OR hard. You need to get your body moving forwards as well as your hand and rackethead.
Think...if you standing on the ground, throw, would your throw go as far as if you stood on a train moving forwards at 10 mph, then you throw?