Add a global setting or button for Fast Previews/Adaptive Resolution. That way users can turn it off globally for an entire project. Currently there is no way to do this except to go in each composition and set fast previews to 'Off (Final Quality)'.

Also, this might be a bug, because for some reason, at a certain moment, this has been turned on and now it is turned on every composition or project I open resulting in a very pixelated preview.