I have a bunch of .NET Webservices running in one IIS Application. These webservices are consumed by another IIS Application (frontend). The first call is pretty slow, about
Not sure if this will solve slow spin up of the WS on the "very first time", as I assume there is a load of compiling and .net DLL's being loaded, but you can almost eliminate any future cold starts by ensuring the application pool the WS is in is configured correctly.
By default, IIS6 has "respawn" on idle, after a number of minutes or "recycle" events that effectively restart the WS each time. If your happy the service is stable then these are not needed.
Ensuring that the WS has it's own dedicated application pool (is not sharing an inappropriate pool) is also a strong recommendation.