No.
Cutting a piece of board into two pieces takes 1 cut. Cutting the board into three takes 2 cuts. If it takes 10 minutes to perform one cut, then two would take 20 minutes.
The marker is dumb enough to think instead that "cutting something into 2 pieces takes 10 minutes. Therefore, that's 1pc per 5 minutes - and 3 pieces must take 15 minutes.
The marker would be right if the question was about cutting pieces off a block of wood - in which case the bulk block would not count as a piece.
edit: well, actually, I take that back.
Yes, it can be 15 depending on how you cut the wood, but that's stupid, since you don't define the method as the quickest possible one, then you can answer with anything you want and justify it.
A scenario to fit the above example could be: the original block was a square. It takes 5 minutes to cut from one edge to the center, and another 5 minutes to do one from another edge in order to cut out a quadrant. Then you only have to spend 5 minutes cutting out a protruding bit to create another piece..