thanks, I did it but didn't work before.
But this time I uninstalled both of dw 2014 1nd 2015, and re installed 2014 only and extension manager. now it is working.
I guess if you have both 2014 and 2015 of dw, the extension manager recognizes both of them as one application and wipe off the extension somehow.
I checked in with adobe and they are updating now and those extensions will work on 2015 with the extension manager but they said they no not recommend to install extensions through the extension manager, they said all depends on third parties and interface issues also depends on them. I don't think that way though. adobe is almost tyrant doing whatever they like and they do not think about long-term users neither third party developers, causing problem every time they make major updates. I am getting sick of it. The update this time is almost terrorism.