Journey trigger taking half an hour or more to process

Journey trigger taking half an hour or more to process

I've set up a journey with the trigger set to someone being added to a list. I have an email that goes out with no delay when the contact is added to the list, but this email typically takes half an hour or more to actually get through processing and sent out.  Ideally, the person would get their welcome email immediately when they join the list. Is there any way to reduce this processing time? Since the welcome email contains information that my contact needs if they don't get it right away they lose interest and end up never logging in. Half an hour to trigger an immediate email is just way to long.