Why do it so complicated? If, on "2.5-day", the release and open beta versions of 1.5 are the same version (like now; 1.5.8.12823.414), you can delete one or the other. It doesn't matter which one, as they are identical at that point. The installer will find your 1.5 and 2.2 files even if they aren't located on the same drive where you are installing 2.5, so if you're low on SSD space, move one or both to a HDD.