The more MultiExcerpt Includes on a page, the greater the degradation in page performance. This is a limitation of Atlassian's Cloud platform that we're, unfortunately, unable to work around at this time. We're hopeful that Atlassian will resolve this limitation in the near future.
We recommend using Confluence Server (version 4 and greater) if possible as it does not have this limitation. There are 3rd party vendors that specialize in hosting Confluence Server (i.e. Contengix) if you don't have an IT department or in house server.