XAP is a file, so when you make a request to a page that require it, this file gets downloaded, so the load time depends on file size and page caching.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items