Tony Vargas
Legend
More to the point, they're choosing to implement a mechanic (Vancian casting) that encourages the 15mad.Here it is discussed that WotC are choosing not to implement a mechanic to counter the 15mad. http://www.enworld.org/forum/new-ho...n-d-d/326541-five-minute-workday-article.html
As you say, there are carrots and there are sticks. Vancian is a carrot - more like an all-you-can-eat buffet - that rewards the 5MWD. Rewards it lavishly /and/ causes radical class imbalance as a bonus (for people who love playing characters that are better than the next guys').
Yes, you could try to beat players away from all that with a stick, or offer them a carrot, but simply taking away the perverse incentive is a much better idea.
In other words, don't try to discourage the 15mwd, just don't encourage it to such an extreme degree.