I regularly walk to the parks from farther away than Holiday Inn. It should take about 15 to 20 minutes at a reasonable pace and my guess is that, during busy periods at least, driving will not save you all that much time.
In fact, why don't you try it out? Have one member of your party walk while the others drive. Meet at the top of the stairs from Valet Parking (just before the last set of moving sidewalks on the way to CityWalk).
If you do, post the results here!