ASP.Net WebMethod is fast on local but works slowly in processing requests on server

I am using the following Web method.. its work fast on local host , but on Domain hosted server .. its works odd , i;e; some time its work fast about (1-3 sec) and some take about 10-14 sec to process..  how do i make it work properly and fast.. and what are possible solution for it..

here is my code

[WebMethod]
    public static string DisplayMessage(string name, string price,string obj, string id)
    {

        SqlConnection conn = new SqlConnection(WebConfigurationManager.ConnectionStrings["eshopConnectionString"].ConnectionString);
        //Creating Delay""
            conn.Open();
     
       
        string emailid =HttpContext.Current.User.Identity.Name;
        string date = DateTime.Now.ToString();
        string s = HttpContext.Current.User.Identity.Name;
        string[] split = s.Split('@');
        string username = split[0];

        SqlCommand cmd1 = new SqlCommand(("select * from cartnew where  productid ='" + id + "'and userid='" + UserId + "' "), conn);
        DataSet dss1 = new DataSet();
        SqlDataAdapter adpr1 = new SqlDataAdapter();
        adpr1.SelectCommand = cmd1;
        adpr1.Fill(dss1);
        
        int k = dss1.Tables[0].Rows.Count;
        if (k == 0)
        {
            string sql = string.Format(@"INSERT INTO [eshop].[dbo].[cartnew]
([prodname]
,[prodprice],[produrl],[userid],[quantity],[productid],[emailid],[username],[date],[subtotal])
VALUES
('{0}'
,'{1}','{2}','{3}','{4}','{5}','{6}','{7}','{8}','{9}')", name, price, obj, UserId, '1', id, emailid, username, date, price);
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = sql;
            cmd.CommandType = CommandType.Text;

            cmd.ExecuteNonQuery();
        }

        else
        {
            SqlCommand cmd2 = new SqlCommand("select * from cartnew where productid ='" + id + "'and userid='" + UserId + "'", conn);
            SqlDataAdapter adp = new SqlDataAdapter();
            adp.SelectCommand = cmd2;
            DataSet ds = new DataSet();
            adp.Fill(ds);
            int val = int.Parse(ds.Tables[0].Rows[0]["quantity"].ToString());
            double p = double.Parse(ds.Tables[0].Rows[0]["prodprice"].ToString());

            string s1 = ds.Tables[0].Rows[0]["productid"].ToString();
            string s2 = ds.Tables[0].Rows[0]["userid"].ToString();

            val = val + 1;
            p = p * val;
            SqlCommand cmd3 = new SqlCommand("update  cartnew set quantity='" + val + "',subtotal='" + p + "' where  productid ='" + s1 + "'and userid='" + s2 + "'", conn);
            cmd3.ExecuteNonQuery();

        }
        conn.Close();
        
        return " ";
     
    }