Mass does not affect speed directly, but it does affect how fast an object can change its speed by accelerating or decelerating. Objects with larger masses require more time for acceleration or deceleration compared to lighter objects.
The law of inertia states that objects that are still remain still and that objects in motion remain in motion regardless of the object's mass. This applies to all moving objects regardless of the speed of movement. The speed stays the same whether the mass is small or large. When a force is applied to either increase or decrease the object's speed, the object's mass comes into play. For any given force, objects with larger masses take longer to change their speeds than objects with lower masses.