The premise of your question is wrong. If you are in Earth orbit, you are moving fast. It's actually being in orbit that allows you to move slowly away, because

The premise of your question is wrong. If you are in Earth orbit, you are moving fast. It's actually being in orbit that allows you to move slowly away, because you can take as long as you want to apply the force. If you're not in orbit you have to quickly apply enough force to escape Earth's influence in one go or you will fall back to Earth.