SetLowRez.cs

public class SetLowRez : MonoBehaviour
{
    [SerializeField] protected bool doOnAwake = true;
    [SerializeField] protected int xRes = 64, yRes = 64;

    private int bigXRes, bigYRes;

    private bool isLowRes;

    private void SetSmallResolution()
    {
        isLowRes = true;
        bigXRes = Screen.currentResolution.width;
        bigYRes = Screen.currentResolution.height;
        Screen.SetResolution(xRes, yRes, true);
    }

    private void SetBigResolution()
    {
        isLowRes = false;
        Screen.SetResolution(bigXRes, bigYRes, true);
    }

    private void Awake()
    {
        if (doOnAwake)
        {
            SetSmallResolution();
        }
    }

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.K))
        {
            if (isLowRes)
            {
                SetBigResolution();
            }
            else
            {
                SetSmallResolution();
            }
        }
    }
}