I suppose there could be a number of reasons why OE might start up very slowly. The most common one I've seen is if the "Compact messages in the background" feature is turned on. To check on this go to the Tools menu, choose Options, select the Maintenance tab, and make sure the checkbox for this feature is unchecked.
Other possibilities would be anti-virus email plug-ins, settings to connect to an ISP automatically when the email client is started, etc.
Hope this helps.
Regards,
Jim
BTW, it is a good idea to compact all the folders manually on a fairly frequent basis. (File | Folders |Compact All Folders)