That’s great actually.

Then I would suggest using used thin clients. They cost around 50€ each, maybe less. You can install a Linux on there and remotely manage them then. They are quiet, small, not energy intensive and mostly have an x86_64 CPU, so software is also not an issue.

They also mostly have HDMI so connecting is not an issue either. If you still buy a Bluetooth remote, they can be handled without a mouse.

Software wise I am not well versed with google slides, but you can probably use kiosk mode in Firefox or chrome and just have the main page with the slides as chosen website.