What do you need $2.5m for?
The correct goal is not the avoidance of work, but the enjoyment of life.
Your proposed goal has a lot in common with winning the lottery: work for 3 years (buy lotto tickets), accumulate (win) $3MM, then never have to work again.
Looking at people who won the lottery, we find many of them go on to have an unhappy life:
http://www.newscientist.com/article/dn16449-lottery-wins-no-...