Hello,
It will be difficult to check in the parent theme. The thing is that the customization that is situated in the Child theme will be saved. Everything that is in the Parent theme will be overridden after the update. If you knew the parts which were overridden in the parent theme, then we could suggest whether it possible to move to the Child theme but if you do not know, it’s difficult as the theme is very big.
In any case, I suggest you move the site to the staging platform and update the staging site to check what exactly you can lose after the update, or maybe everything is in the Child theme and you will not lose anything.
Kind Regards