Only show integers on a slider

I have a slider question on which I'd like respondents to choose from the quarter hour. I have the question configured to meet my needs, but I would like the slider to only display integers for the grid marks. Right now, the grid is illegible due to the number of grid marks. I have found the code to only show integers and the halves (1, 1.5, 2, 2.5) but I would prefer to only show the whole numbers.