Report Viewer slow in ASP.NET

I have a page with a Report Viewer in ASP.NET. When I built the report in SSRS, it was fast (taking 1-3 seconds).

Saving it as PDF or EXCEL is also fast:

Private Sub SetReportParameters()
    'Set Processing Mode
    ReportViewer1.ProcessingMode = Microsoft.Reporting.WebForms.ProcessingMode.Remote
    'Set report server and report path
    ReportViewer1.ServerReport.ReportServerUrl = _
       New Uri("xxx")

    ReportViewer1.ServerReport.ReportPath = _
       "xxx"

    Dim paramList As New Generic.List(Of ReportParameter)
    Dim pInfo As ReportParameterInfoCollection
    pInfo = ReportViewer1.ServerReport.GetParameters()

    'if you have report parameters - add them here
    paramList.Add(New ReportParameter("xxx", "xxx", True))
    ReportViewer1.ServerReport.SetParameters(paramList)

    'Process and render the report
    ReportViewer1.ServerReport.Refresh()


    'output as PDF
    Dim returnValue As Byte()
    Dim format As String = "EXCEL"
    Dim deviceinfo As String = ""
    Dim mimeType As String = ""
    Dim encoding As String = ""
    Dim extension As String = "xls"
    Dim streams As String() = Nothing
    Dim warnings As Microsoft.Reporting.WebForms.Warning() = Nothing

    returnValue = ReportViewer1.ServerReport.Render(format, deviceinfo, mimeType, encoding, extension, streams, warnings)
    Response.Buffer = True
    Response.Clear()

    Response.ContentType = mimeType

    Response.AddHeader("content-disposition", "attachment; filename=xxx.xls")
    Response.BinaryWrite(returnValue)
    Response.Flush()
    Response.End()
End Sub

But, if I want to show it in the page, it is TOO slow (taking more the 10 minutes to render).

Private Sub SetReportParameters()
    'Set Processing Mode
    ReportViewer1.ProcessingMode = Microsoft.Reporting.WebForms.ProcessingMode.Remote
    'Set report server and report path
    ReportViewer1.ServerReport.ReportServerUrl = _
       New Uri("xxx")

    ReportViewer1.ServerReport.ReportPath = _
       "xxx"

    Dim paramList As New Generic.List(Of ReportParameter)
    Dim pInfo As ReportParameterInfoCollection
    pInfo = ReportViewer1.ServerReport.GetParameters()

    'if you have report parameters - add them here
    paramList.Add(New ReportParameter("xxx", "xxx", True))
    ReportViewer1.ServerReport.SetParameters(paramList)

    'Process and render the report
    ReportViewer1.ServerReport.Refresh()
End Sub

I am using:

• SQL Server 2012


• .NET Framework 4.5

What am I doing wrong?