What's the penalty exp on past lives while leveling a different life?

In Fantasy Life your job is referred to as your Life. You can swap between them at will by visiting the guild master and asking to change but he mentions that your skills from past lives will not level as fast as they would if they were your current life. How much slower is what I am wondering as there are some jobs I would like to have access to the skills but may not really need to level them up at a faster rate.