I suppose you are talking about Photos.
I don't think there are any options to select besides what the music is and the type of slideshow to use, among the choices presented.
That said, when doing a slideshow from an album or a selection of photos, for me it always plays them in the order they are in the current view (e.g. sorted by oldest first, newest first or by name).
I think Photos is only ok for this if you only need a quick and simple slideshow, but is not meant for a very sophisticated one.
You could try iMovie, where you have all the flexibility of a video editor but will need to do more work, or use a third party application like FotoMagico, which is supposedly made for slideshows, with all the bells and whistles.