The KDE desktop uses quite a lot of effects (transparency, glowing things, blur etc). You should be able to speed up login by disabling the Login splash screen, as well as extra effect under 'Desktop Effects' > 'All Effects', extra services under 'Startup and Shutdown' > 'Seervice Manager', and by reducing resource usage under 'Application Apperance' > 'Style' > 'Fine tuning'.
This page in the Ubuntu wiki may help, which suggests installing the latest updates and disabling the effects.
As @bodhiz.zazen suggests, using a interface such as webmin may be better for the running of a server. Another lighter environment (without unnecessary effects) such as Xfce or LXDE may also work faster.