Unfortunately there is no lazy-loading option for the current version of RadCoverFlow. We plan to include UI virtualization in one of our next releases, but I cannot promise you an exact date. To optimize the current performance you can turn off both the loading animation and the reflection that are rendered for every item. I hope this will partially resolve your problems.
Excuse us for this inconvenience, and I hope this will not be a show stopper for you.
the Telerik team