This issue appears to be related to the new graphics system (HG2) introduced in MATLAB R2014b. The "contourf" function takes longer to render contour plots than it did in the old graphics system of previous releases.
A workaround for this issue is to instead use the "imagesc" function to display the image. This renders the image data very quickly and handles "ginput" events and other user interaction much better than a contour plot does. Additionally, for applications where some form of real-world scaling matters, the "imagesc" function provides properties 'XData' and 'YData' that allow the user to position the image in data coordinates to match the desired scaling.
The provided workaround script ('example_imagesc.m') performs the same task as the other provided script, except it uses "imagesc" instead of "contourf" to display the image data. Running the two scripts clearly shows that the "imagesc" function is much faster for displaying image data in this manner.