I don't play vanilla minecraft so I don't know what the launcher looks like anymore but if you can find the settings tab in the launcher and make sure you've got an optimal amount of max RAM available to use and make sure it hasn't set itself to something stupidly low for some reason, that's something I suggest trying.

I don't play vanilla minecraft so I don't know what the launcher looks like anymore but if you can find the settings tab in the launcher and make sure you've got an optimal amount of max RAM available to use and make sure it hasn't set itself to something stupidly low for some reason, that's something I suggest trying.