Web Service slows down

Public Class GRV
    Inherits System.Web.Services.WebService
    Dim bus As New GRBussiness

    <webmethod()> _
    Public Function HelloWorld(ByVal strShippingLabel As String, ByVal strBoxStatus As String, ByVal strWeekNo As String) As Boolean
        Dim ShippingLabelisFound As Boolean = False
        Try
            ShippingLabelisFound = bus.Scan_MarkShippingLabelsFound(strShippingLabel, strWeekNo, strBoxStatus)
            Return ShippingLabelisFound
        Catch ex As Exception
            Return False
        End Try
    End Function
End Class

Sub MakeConnect_GRV()
        GRVcon.ConnectionString = "Data Source=192.168.10.24\BDMS;" & _
                                       "Initial Catalog=FLATPAN_STOCK;" & _
                                       "User ID=flatpan;" & _
                                       "Password="password"
        Try
            GRVcon.Open()
        Catch ex As Exception
            'MessageBox.Show(ex.Message)
        End Try
    End Sub
Sub DestroyConnection()
        GRVcon.Dispose()
    End Sub

Function Scan_MarkShippingLabelsFound(ByVal ScanndedShippingLabel As String, ByVal WeekLookup As String, ByVal strBoxStatus As String) As Boolean
 
Try
  Dim ShippingLabebelStatusIsUpdated As Boolean
  Dim strUpdate As String = ""
  If ScanndedShippingLabel <> "" And strBoxStatus <> "" Then
    If WeekLookup = "" Then
     
     strUpdate = "Update PackingLists " & _
       "Set BoxStatus=@BoxStatus, ScanDate=@ScanDate " & _
       "WHERE ShippingLabel='" & ScanndedShippingLabel & "' " & _
       "AND BoxStatus='" & strBoxStatus & "'"

    Else

     strUpdate = "Update PackingLists " & _
     "Set BoxStatus=@BoxStatus, ScanDate=@ScanDate " & _
     "WHERE ShippingLabel='" & ScanndedShippingLabel & "' " & _
     "AND WeekNo='" & WeekLookup & "' AND BoxStatus='"      strBoxStatus & "'"

    End If

  If data.grvConnection.State = ConnectionState.Closed Then _
   data.MakeConnect_GRV()

Dim cmdEdit As New SqlClient.SqlCommand(strUpdate, data.grvConnection)
cmdEdit.Parameters.Add("@BoxStatus", SqlDbType.VarChar,50).Value="FOUND"
cmdEdit.Parameters.Add("@ScanDate", SqlDbType.VarChar,50).Value=Date.Now

Dim IsRowadded As Integer = 0 'Variable to check if row is added
If data.grvConnection.State = ConnectionState.Closed  Then data.grvConnection.Open()
   
IsRowadded = cmdEdit.ExecuteNonQuery()
   If IsRowadded = 1 Or IsRowadded > 1 Then
    ShippingLabebelStatusIsUpdated = True
   Else
    ShippingLabebelStatusIsUpdated = False
   End If
    cmdEdit.Dispose()
data.DestroyConnection() ' just added this now and will test...
   End If
    Return ShippingLabebelStatusIsUpdated
   Catch ex As Exception
  'MessageBox.Show("GRBusiness:- MarkShippingLabelsFound: " & ex.Message)
            Return False
        End Try
    End Function

DestroyConnection()        
GRVcon.Dispose()    
End Sub