Can you provide more details? Are your documents (events) guaranteed or volatile? Do sub2 and sub3 use any of the same resources as the OrderProcess?
Mark
Using volatile documents should be faster than using guaranteed ones. The broker will take longer to process guaranteed documents because each one has to be written to disk. If the server has slow disk subsystem this can create a performance bottleneck.
If guaranteed documents are required to meet reliability requirements, consider using fast disks or disk controllers with onboard cache. Sometimes the use of well designed RAID configurations can help as well.
Mark