"Actually ..." You may recall that the Mercury mission took several years and several planetary flybys to get there. If you don't need to go fast (a crewed mission normally WOULD go fast, to limit supplies needed and radiation exposure), it takes a lot less fuel: en.wikipedia.org/wiki/Interpl...

Interplanetary Transport Network - Wikipedia

The total energy required is the same, it just differs where you get it from (fuel vs gravity assists)