How many requests made by shoutbox to a single user. If there are 30 shouts in myshoutbox (by pirata nervo V1.5 )
admin has debug information on every page of myBB ; if you have not turned it OFF then
you have to analyze from advanced details of debug information OR check it on server logs
don't have a single page with only shoutbox on it
^ you can try forumURL/index.php?action=full_shoutbox&debug=1