I need to make a Sphere appear 15 seconds after the FPSController has collided with a Cube and then make the Cube disappear after 30 seconds.

Ask if you need any specific details or clarifications. My english isn’t the best sorry. I am using C#.

public GameObject prefabSphere;

	void OnCollisionEnter(Collision other)
	{
		if(other.gameObject.CompareTag("Player"))
		{
			StartCoroutine("SpawnAndDie");
		}
	}

	IEnumerator SpawnAndDie()
	{
		yield return new WaitForSeconds(15f);
		Instantiate(prefabSphere);
		yield return new WaitForSeconds(15f);
		Destroy(gameObject);
	}

Really basic, but should get you started.