I just tried Google Play on my Sharp Roku TV. The channel itself loaded in a few seconds. I then moved to my library and selected a movie to play. This too was running in a matter of seconds.
I just timed it from pressing the button to the channel being fully loaded and ready to select something. 5 seconds. I doubt the size of your library has anything to do with loading the channel, because I noticed it had to load my library separately when I selected it. I only have 29 titles in there.