I have experienced this dozens of times at the conferences I have hosted. Presenters try to send in PPT files that are 50MB and larger.
Quite often, this occurs with real estate, oil & gas and drilling firms. Their presentations tend to include many high-res arial photographs and maps. This will not affect the visual "screen" or projected resolution display.
Click on your inserted photo to activate the compress function, upper left. Sorry, there is not delete funny people function.