Website slowness when using SignalR for notifications

Good morning, I'm developing a site to run in local intranet format on IIS . With asp.net ADO technologies in the WebForms format, I'm using the SignalR library to monitor a simple table in SQL Server Express via SqlDependency , which shows clients as real-time notifications equal to the top of the stackoverflow site. The users are authenticated in the site via authentication Forms , the implementation is functional but when the site is started it will be slow and slow until the locking. I imagine that the flow of calls to the bank is congesting the network / IIS. Look at the implementation code, if anyone can point out what is causing the slowness.

Hub class:

using Microsoft.AspNet.SignalR;
using Microsoft.AspNet.SignalR.Hubs;

namespace ZaniADV
{
    [HubName("MyHub")]
    public class MyHub : Hub
    {
        public static void Show()
        {
            IHubContext context = 
                GlobalHost.ConnectionManager.GetHubContext<MyHub>();
            context.Clients.All.displayStatus();
        }
    }
}

Statup class:

using Microsoft.Owin;
using Owin;
using Microsoft.AspNet.SignalR;

[assembly: OwinStartup(typeof(ZaniADV.Startup))]

namespace ZaniADV
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {            
            GlobalHost.Configuration.DefaultMessageBufferSize = 500;

            app.MapSignalR();
        }
    }
}

Global.asax

namespace ZaniADV
{
    public class Global : System.Web.HttpApplication
    {
        protected void Application_Start(object sender, EventArgs e)
        {
            SqlDependency.Start(ConfigurationManager.ConnectionStrings
                ["MyConnectionString"].ConnectionString);
        }

        protected void Application_End()
        {
            SqlDependency.Stop(ConfigurationManager.ConnectionStrings
                ["MyConnectionString"].ConnectionString);
        }
    }
}

Code-Behind page MenuNotification.aspx.cs

        [WebMethod]
        public static IEnumerable<Inbox> GetData()
        {
            using (var connection = new SqlConnection
                (ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString))
            {
                connection.Open();
                using (var command = new SqlCommand(@"SELECT [IndexID],                        
                        [Numero] FROM [AdvogadoDB].[dbo].[IndexA] WHERE [AdvogadoID] =" + 
                        AdvogadoCRUD.ReturnAdvogadoID((Guid)Membership.GetUser().ProviderUserKey),
                        connection))

                {
                    command.Notification = null;

                    SqlDependency.Start(
                        ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString);
                    SqlDependency dependency = new SqlDependency(command);
                    dependency.OnChange += new OnChangeEventHandler(dependency_OnChange);

                    if (connection.State == System.Data.ConnectionState.Closed)
                        connection.Open();

                    using (var reader = command.ExecuteReader())
                        return reader.Cast<IDataRecord>()
                            .Select(x => new Inbox()
                            {
                                Numero = x.GetInt32(1),                                                   

                            }).ToList();
                }
            }
        }

        private static void dependency_OnChange(
            object sender, SqlNotificationEventArgs e)
        {
            MyHub.Show();
        }
    }
}

Customer javascript code page MenuNotification.aspx:

<script src="Scripts/jquery-3.1.1.min.js"></script>
<script src="Scripts/jquery.signalR-2.2.2.js"></script>
<script src='<%= ResolveClientUrl("~/signalr/hubs") %>'></script>

        <script type="text/javascript">

        $(function () {
            var job = $.connection.MyHub;

            job.client.displayStatus = function () {
                getData();
            };

            $.connection.hub.start();
            getData();
        });

        function getData() {
            var $inbox = $('#inbox');
            $.ajax({
                url: 'MenuNotification.aspx/GetData',
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                type: "POST",
                success: function (data) {
                    //debugger;
                    if (data.d.length > 0) {
                        $inbox.empty();
                        var newdata = data.d;
                         var rows = [];
                        for (var i = 0; i < newdata.length; i++) {
                            rows.push(newdata[i].Numero);
                        }
                        $inbox.append(rows.join(''));
                    }
                }
            });
        }

    </script> 

                <li class="dropdown tasks-menu"
                    data-toggle="tooltip" data-placement="bottom"
                    title="Últimas mensagens no inbox">
                    <a href="/ZaniADV/Views/Designar.aspx" target="_parent"
                        class="dropdown-toggle" data-toggle="dropdown">
                        <img src="/ZaniADV/Image/inbox.png" />
                        <label id="inbox" class="label label-danger" 
                            style="font-size: 12px"></label>
                    </a>
                </li>

Table BD:

ALTERDATABASEAdvocateBDSETENABLE_BROKER

Finalresult:

Client1:

Client2:

ResourceMonitor:

Memory:

CPU:

Network: