Here's the query:

Code
select t1.USER_DISPLAY_NAME,count(t2.POST_ID) as total 
from ubbt_POSTS as t2, 
ubbt_USERS as t1 
where length(t2.POST_BODY) < 15 
and t1.USER_ID = t2.USER_ID 
group by t2.USER_ID 
having total > 5 
order by total desc 
limit 11