>>you can try to copy the correct native dll to the output folder
I succeeded to run both Tobii sdk and other 64bit dll under 64 config app.
I checked projectfolfer/bin/debug/Tobii.EyeX.Client.dll. It was 32bit. I copied 64bit Tobii.EyeX.Client.dll to the folder.
Then my app run as 64 bit.
That must be a bug of Visual Studio 2015.
Thanks for a long effort of your support.