If you have the same problem, check out the kopete related bug report #119529:
The statistics plugin takes *ages* to start.
And there it is: the main reason why kopete takes so much time is that a specific plugin, the statistics plugin, needs so much time, and therefore blocks kopete everytime it comes up or has to be closed.
I deactivated it, and the problem was gone, kopete starts in seconds and closes in seconds.
If you wonder for what you need the plugin: well, it can provide you with a set of interesting usage statistics of your contacts: how long they are online, offline, away and so on while you are online.
When you really need it, well, poor you, in other cases: nice to play around with, but don’t forget to deactivate it for the daily usage of kopete.
Another option would be to change its code to a less time consuming way of working, but at the moment there is no one working on that afaik.