Patterns for Deleting large amounts of data
but you are missing RequestID 
hopefully you have index on URLID  and RequestID 

select 1 
while (@@rowcount &gt; 0)
BEGIN
  DELETE TOP (50000) b 
  FROM TableB b 
  JOIN TableA a
    ON b.URLID = a.URLID 
   AND a.RequestID = @RequestID
END


Disable FK can help but be sure you are not breaking any FK