Integrated fins on a can are almost ALWAYS more efficient at cooling. Using a heat sink on a CC NEU you would only be getting 1/2 of the contact surface area. The space between the CCNeu fins would just be void space filled with insulating air because it wouldn't be moving away from the motor.
15min at 165? Better than I can claim on really conservative gearing and driving. If you want better temps, change your gearing, your driving habits, or wait for cooler weather