The World Map Kit Online applies the tile cache. All the tile images have been pre-generated using the MapSuiteTileCacheGenerator in advance, in other words, for the cached image, it just reads the tile images from disk instead of drawing them on the fly. You can download the MapSuiteTileCacheGenrator tool at here, if it's necessary. The tool is based on the Version 8.0, so if the version 9.0 is used on your side it will get a error during compiling, you just only change the "Integer" to "Numeric" to make it right.
There are two options to improve the performance.
1. Applying the tile cache to LayerOverlay by setting the “TileCache” property of overlay to cache the tile locally.
2. Setting the “TileType” of overlay as MultiplyTile to draw tile by multithreading.
More information about “TileCache” at here.
Hope it's helped.