I can’t remember how expensive videomaps really are and in what way, i.e. whether the whole thing goes into video RAM, or if the required video frame is decompressed and loaded to the card each frame, or something else. I know that when they were first introduced in Quake 3: Team Arena, the a cvar to disable their rendering was included as a video menu option, so they must have been considered pretty fat back then. (The min spec for Q3:TA was something like PII 350MHz, 64MB RAM, 8MB graphics though)
My main concern would be whether it’s worth adding 3MB to your pk3 size just for it? (Plus I guess a chunky sound file for the projector too)
Perhaps a nice alternative might be to construct a slideshow effect using an animap stage. You could even use some existing images for it, such as the map loading screens or something like that.