You should also look at how you are downloading the posters. Using roscreen or roimagecanvas won't improve the actual transfers between your server and the channel.
I'd suggest downloading your 10 initial posters as you have been, but then, in the background, download more posters using asynchronous transfer so they download in the background while still allowing the user to do something on the interface.
You can also consider a paging system - where you download 10 posters or so, and then add an option for "show more" - when the user clicks that, download another 10 posters as needed.
How big are the posters compared to the size they're being drawn on screen? If they have to be scaled every time, then that will slow things down considerably, so it's best to use native sizes. You can test to see if that's the issue pretty quickly by repeating your loading poster test with a poster that's the right size.