RadComboBox with large data MVVM

[moe]

Hello, 

I have this combobox with is bound to List of customers around 5k customers

<telerik:RadComboBox ClearSelectionButtonVisibility="Visible" ClearSelectionButtonContent="Clear Selection"
                                     ItemsSource="{Binding Customers}"  Margin="0 0 0 18"
                                     DisplayMemberPath="DisplayMember"
                                     SelectedValuePath="Id"
                                     SelectedValue="{Binding CustomerId,Mode=OneWay}"
                                     Command="{Binding GetCustomerCommand}">
                    <telerik:RadComboBox.ItemsPanel>
                        <ItemsPanelTemplate>
                            <VirtualizingStackPanel />
                        </ItemsPanelTemplate>
                    </telerik:RadComboBox.ItemsPanel>
</telerik:RadComboBox>

 

 

I changed to virtualization and this helped in getting the list faster but when I added SelectedValue to bind to my viewmodel It is getting very very slow to load.

Is there any way to overcome this problem ?

Regards