Microsoft's NETMF support for VS2015 is still in beta, but I'm running it here without issues.
Please try this:
1. Close all instances of Visual Studio.
2. Uninstall the Netduino SDK
3. Uninstall the NETMF SDK
4. Make sure that VS2015 is installed on your computer.
5. Install the NETMF 4.3 QFE2 SDK (from the downloads page)
6. Install the NETMF plug-in for VS2015 (alpha) from here: http://netmf.codeple...ads/get/1423121
7. Install the Netduino SDK
Alternatively, if you haven't installed the NETMF plug-in for VS2015 (alpha)...try that first. If that fails, then go ahead and follow the full "uninstall and reinstall" procedure outlined above.
Does that get you up and running?