you should check this link:
This should be very helpful.
Extension Builder 2.1 works with CS5-CS6.
Sorry. I also ment Extension Builder 3 ...
I don't think it works with 2015!
You can make it works with CC2015. But you need to tweak it as explained:
note: this is for 2014, but you can do it for 2015 swell.
But forget about Eclipse and Extension Builder 3,0. (not efficient).
You should use Brackets, WebStrom or whatever.
Create your project template, create and edit manifest.xml, develop your extension.
You could also create scripts or tasks (gulps) to automate tasks (copy, sign, install, ....).
And this is it!