I know there's a lot you can do in VS2015 as far as cross platform mobile dev, but I am not sure if it can do Linux, specifically for the Raspberry Pi Raspbian OS. Can it?
If not, can I use something like Eclipse on my Mac or something else on my Windows machine?
I've done some mobile work before in iOS and a tiny bit of exploration in Droid so I imagine it's close to one of those.
Yes you can.
Raspian is a pretty complete OS, so you could run apps compiled by any language like Python/node/C/C++/C#. (Raspberry Pi 2 can now run Ubuntu)
Run Windows Apps
The easiest way to do it would be to load Windows IoT Core onto Raspberry Pi and create UWP apps in Visual Studio. This gives you remote deployment, debugging and powerful APIs from the get go. Windows Iot Core for Raspberry Pi
Python & Node
Write in VS using nodejstools python tools Then you just copy paste the code to rpi, and run it using node/python
C/C++
Simply use VS to develop, and build using the Windows toolchain for Raspberry Pi.
C#
I haven't played around it too much, try mono