As per the Cast SDK Docs, to use Cast SDK in Android I need, Google Play Services Revision 15.
I dont see Rev 15 in my SDK Manager. Can anyone else see it yet? or know by when we can expect to start developing for Android with rev 15? Is there an alternative stop gap to get around the problem till Google pushes out to all SDK Managers?
Can anyone else see it yet?
No, because it is not yet available.
UPDATE: OK, now it is. Let the downloading commence!
or know by when we can expect to start developing for Android with rev 15?
On the page that you linked to, in a large yellow box, you will find:
Developing with the Google Cast Android APIs requires Google Play services 4.2, which began rolling out to devices worldwide on February 3rd. Once the update to devices is complete, the corresponding Google Play services library (revision 15) will be available for download from the Android SDK Manager.
(emphasis added for emphasis, emphatically)
Note that today is February 3rd, which means the Play Services rollout just began today.
Is there an alternative stop gap to get around the problem till Google pushes out to all SDK Managers?
You can wait patiently. Or wait impatiently, if you prefer.