If they are Kodachromes projecting for a minute or two will not result in a detectible change in density or color shift. I have projected some for up to a half hour for doing pastel drawings with no noticeable change. I think you'd need several hours of exposure to projector light to see really measurable differences.

With dark storage my older Kodachromes begin to fade at around 40 years depending on who did the processing.

Tom1956 many posters are done using notoriously poor non archival ink so are absolutely subject to fading rapidly in sunlight and even subdued light.

Nate Potter, Austin TX.