Despite LEDs being a much cooler illumination than conventional bulbs, they do nonetheless heat up. The brighter the LEDs, the more heat produced. The VISIO projectors have passive cooling that draws heat away from the LED to improve longevity, but still get hot to the touch.
There is no cooling at all of the slide, so this will heat up. The slide mount used for the VISIO projector use inexpensive slide mounts for economy, and if allowed to heat up the thin plastic may distort and the film may ripple too.
Note that neither the slide mount nor the film will melt or catch fire, but there will be distortion under some circumstances, particularly if run continuously for three or four hours. When used outside on a winter’s night this all may not be a problem.