This worked for me. [ Thanks to +Tyrel Parker @Google+ ]
... This API packages contain a single tar.gz file and the post install script of the package puts the content of this tar.gz to the right place and wires it in, in the way it should be. Once the package is installed the new Kit will be automatically recognized by the IDE.
How to test these packages?
$ sudo add-apt-repository ppa:ubuntu-sdk-team/tools-development -y
$ sudo apt-get update
$ sudo apt-get install ubuntu-sdk-ide ubuntu-sdk-api-tools
$ sudo apt-get install ubuntu-sdk-api-15.04-armhf ubuntu-sdk-api-15.04-i386
After that look for the "Ubuntu SDK IDE" in the dash.