I created a sample project from your description - a TileViewItem with 10 images, 6 textblocks and a button and it is performing ok according to me. With UI Virtualization it's normal to have a some lag when you scroll because if you scroll fast at some moment the RadTileView will have to generate 3-4 rows or 21 - 28 RadTileViewItems which is a lot.
You may increase the performance by decreasing the number of tiles in a row - this means less containers for generating on scrolling.
Also if the loading time without virtualization is not very long (1-2 secs) you may try to use the RadTileView without the virtualization.
I've attached the my sample project and if you have more questions please feel free to ask.
the Telerik team
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