By Adam Nagy
The easiest way to check which .NET Framework version Inventor or other products are using is by looking into their config file. In case of Inventor 2015 it's "C:\Program Files\Autodesk\Inventor 2015\Bin\Inventor.exe.config"
There you'll find the <startup> tag. In case of Inventor 2015 it has the following content, which shows it's using v4.5:
Based on that you should use a Visual Studio version that supports the given version of the .NET Framework.
Visual Studio versions so far have been backward compatible, so if you have a newer version that could be used to create a project that uses an older .NET Framework. E.g. Visual Studio 2012 offers the following: