First take a look at your server's debug log to see the actual times involved and to see if anything stands out.
"Probing" is likely one area where your startup time can be improved. By default DevForce will look through all assemblies in the bin folder for everything it needs - which is entity models, DevForce interface implementations, and known types. If a lot of assemblies are being probed or the elapsed time is long, you can use the CompositionHost.SearchPatterns to control what is searched. Here's more info -
http://drc.ideablade.com/xwiki/bin/view/Documentation/CompositionHost