How to delete video file previews when connected to a screen

So. I have a ton of porn. On my plex server. I also like to play movies for my kids on occasion. How to I stop or block video previews of specific libraries from being randomly displayed while Plex is connected to the chromecast, but not actively playing a file?

I have "Generate video preview thumbnails" by setting it to "Never" and clicking the DELETE PREVIEW THUMBNAILS in each library, but they still show up. I'm guessing they aren't the same thing?

Any help?