Is it just the first load of the login that is slow?
- Login [yes, I know it's slow]
- Login again [is it fast this time?]
IIS, by default, will put an application to sleep if its unused for several minutes (20 minutes I think). Using the test above, if the 2nd login is fast then this is probably what is happening. (You can ping the application every 15 minutes or so to keep the application alive.)
On the other hand, if the 2nd login is still slow then something else is going on. How many Sitefinity pages do you have? What types of custom have you added? Are you using shared hosting?
Telerik | Sitefinity CMS