Why VS2015 intellisense shows error on C++11 user defined literals (UDL)

The below code can be compiled and run, but VS2015 intellisense shows error. g++ & eclipse has the same issue (compiled & run but shows error)

Does anyone know to fix it. I tried searching on google but couldn't find the answer. The error is a little annoying.. :-)

int main()
{
    this_thread::sleep_for(5s);
    cout << "test \n";

    return 0;
}

Thanks a lot!