Here's how you can build your current project with a single key press in VS!
This means you can build just your current project and not rebuild the whole Engine
I tested this using the compiled version of UE4 (Thank You Epic!)
Go to Tools->Options->Keyboard
and find BuildOnlySelection
Pick your hotkey
Then hit assign!
Open Current Project Build.cs
or any other file that is part of the project you want to build.
Make sure, if there are other builds with files open,
that the project you want to build for has a file that has your input focus
Press Your Chosen Hotkey