This is where i've read someone going back to v1.2, unfortunately he doesn't tell how he got back.
http://forums.eagle.ru/showthread.php?t=159082&highlight=back+to+1.2&page=2
Maybe you can PM him, he doesn't seem to react to the already asked question.
@BIGNEWY, isn't the v1.2 still available somewhere for people that found out too late they can't run v1.5+?
If you would only need the DCS_World_1.2.16.xxx.exe like mentioned in a previous post there, i still got it and that's only 2.7Mb. You can run it 10 times through www.virustotal.com to make sure it's clean.