If you have 2.5 open beta installed and working correctly then yes, you can delete everything else. There is the option to keep 1.5 release version if you so wish but it will not be fully supported beyond limited patching to fix breaking issues... no new planes. The 2.2 open alpha is dead and will not be supported at all. 2.5 open beta will be used to populate the 2.5 release version when ED decide to send it.

For me, I got rid of 2.2 on the release day and will be deleting 1.5 shortly. They are not needed after the 2.5 open beta is downloaded.