The question is if you need to loop a series of slides, or if you are showing each slide for a longer period of time. For looping you will need a carousel, but with 10-15 slides, you will have a lot of blank spaces.
I used to have little Leitz projector (an earlier pradovit, 60-70's), that took straight trays, but only had manual advance. It was not the brightest projector, but it did have an almost in-audable fan. I used to use it for showing a single image projected for a period of time.
I also have a rollei twin, which also takes straight trays. It auto cross fades each slide. You can set the duration that it shows each slide. It is a great projector, but you would need someone there to set it back to the beginning.