How to optimize PlexServer and iPad Player config to view photos



I switched from DS Photo to Plex Server. Plex runs on a decent machine with i3, 4GB RAM and SSD for the Plex library. Now I'm using the Plex player on an iPad air, but with disappointing (photo viewing) performance:
The thumbnails appear very quickly, but when swiping through the photos I almost always see a spinner and wait several seconds for the image to appear. This was never the case with DS Photo on a much slower server hw.
Now, is there a way to optimize the config on the server in a way that this can be improved?
Any idea, what slows this process down?


I am also interested, if there is a way to let Plex create different "transcoded" versions of photos for iPad, iPhone and web viewing in advance to speed up display.