Destroying a Prefab, but I only want to destroy its clone after a certain amount of seconds. How would I do this?

I am still pretty new coding and I added this destruction script to the Bullet but I made it once fired after a certain amount of seconds, the prefab would destroy itself, Im only wanting to destroy the clone any ideas?
My Script:

  public class BulletDestroy : MonoBehaviour {
    	void Update () 
    	{
    		if (Input.GetButtonDown ("Fire1")) 
    		{
    			Destroy (gameObject, 1.5f);
    		}
    	}
    }

Looking at your code it looks like it is attached to your prefab (the gun I guess).

If you want to destroy the bullet after it is fired then attach below script to your bullet prefab.

public class BulletDestroy : MonoBehaviour {

     void Start () 
     {
             Destroy (gameObject, 1.5f);
     }
}

// Pistol.cs, attach to your weapon GO
public class Pistol : MonoBehaviour {
public GameObject bulletPrefab; // drag here a reference to the bullet GO you want to instantiate

    void Update () {
        if (Input.GetButton ("Fire1"))
            Instantiate (bulletPrefab); // you can adjust position and rotation here
    }
}

// BulletDestroy.cs, attach to your bullet GO
public class BulletDestroy : MonoBehaviour {
    void Start () {
        Destroy (gameObject ,1.5f);
    }
}