I'm experiencing a very slow performance while filling a combobox, is this normal?

I'm reading a db with 78000+ rows, it's indexed in those fields i'm filtering.

Here is the code i'm using:

Code:
Dim conn As SqlCeConnection = Nothing
        If cmbMarca.SelectedIndex > 0 Then
            If cmbMarca.Text = "" Then Exit Sub
            Try

                conn = New SqlCeConnection("Data Source = " & GetAppPath() & "\DBs\Artigos.sdf")
                conn.Open()
                Application.DoEvents()
                Dim cmd As SqlCeCommand = conn.CreateCommand()
                Label1.Visible = True
                Cursor.Current = Cursors.WaitCursor

                Dim ceda As SqlCeDataAdapter = New SqlCeDataAdapter("SELECT DISTINCT Modelo FROM Artigos WHERE Marca='" & cmbMarca.Text & "' ORDER BY Modelo ASC", conn)
                Dim ds As New DataSet
                Application.DoEvents()

                ceda.Fill(ds, "Modelo")
                Application.DoEvents()
                cmbModelos.DataSource = ds.Tables("Modelo").DefaultView
                Application.DoEvents()
                cmbModelos.DisplayMember = "Modelo"
                Application.DoEvents()
                Cursor.Current = Cursors.Default
            Catch err As Exception
                MessageBox.Show(err.Message)
            Finally
                conn.Close()
            End Try
        End If
Fields "Marca" and "Modelo" are both primary keys

It's taking more then 4 minutes to return only 2 values from the database..