Slower yes, but not drastically:

    % python -m timeit '{"key": "value", "dr_nic": "The Comedian", "ttl": 42}'
    1000000 loops, best of 3: 0.296 usec per loop

    % python -m timeit 'dict(key="value", dr_nic="The Comedian", ttl=42)'
    1000000 loops, best of 3: 0.771 usec per loop

There are far better ways to make code faster than worrying about the extra fraction of a microsecond you're spending calling dict rather than using the literal syntax.