My team is running into issues with Slideshow Overlays making our InDesign .article files very large. According to the Adobe Help article Optimize content used in Experience Manager Mobile apps, Slideshow Overlays are supposed to automatically be resampled so we shouldn't have to worry about the file sizes of the images used. Is this no longer the case, and we now have to manually optimize our images?
Each Slideshow is set up as a MSO with a button trigger, and there is only one Slideshow in each .article file.
They still are resampled. Images you use in the slideshow will be converted to png and optimised when exporting to .article format. If you were to break open the article file, you'd see an \OverlayResources folder where the optimised images are.
However the overall size of the article will depend on how many photos you have in the slideshow and how much space they take on the page.
I created a slideshow that takes half of my page with JPG images at 16Mb. They are resampled at around 700 - 800Kb. If I reduce the size of the slideshow to about a quarter or the size, those PNG files will be around 160 - 200Kb.