Where can I find local installation files? I'm rather new to Android development. 
Where I work there are pretty tight security measures (firewall etc) preventing me to download API 15 from within Eclipse. We configured Eclipse's proxy settings to match IE's, but this didn't fix the issue. Finally, I took my laptop home to circumvent the issue. Everything works great now, except for the fact that my colleague has a company desktop and needs to work with android as well. Does anyone have any suggestions on how to perform an update on his pc? / Does anyone know in what system folder the Android SDK stores the API15 installation files?

Thanks alot!
I know it's off topic, but the instructions are on the Android developer pages here. See the section under &quot;Troubleshooting ADT Installation&quot;.

If you are still unable to use Eclipse to download the ADT plugin as a remote update site, you can download the ADT zip file to your local machine and manually install it:

Download the current ADT Plugin zip file from the table below (do not unpack it).
Follow steps 1 and 2 in the default install instructions (above).
In the Add Site dialog, click Archive.
Browse and select the downloaded zip file.
Enter a name for the local update site (e.g., &quot;Android Plugin&quot;) in the &quot;Name&quot; field.
Click OK.
Follow the remaining procedures as listed for default installation above, starting from step 4.

To update your plugin once you've installed using the zip file, you will have to follow these steps again instead of the default update instructions.

Just download the zip file to a USB drive, follow these instructions and you're good to go!