How to Restore the Old Game of a Minecraft World?

I accidentally started one of my Minecraft worlds (version 1.15) in version 1.14.4, and now everything has disappeared. Is there a way to load a previous memory? There's a lot of time and effort in the project, so I would be happy to receive a quick response!

Hi, it happened to me sometimes - really stupid… Unfortunately you can't restore it unless you have made a backup beforehand.

Not at all