As you said, the TMC is updated everytime there is a tape event (OPEN/CLOSE/EOV as well as a CATALOG/UN-CATALOG event). And, everytime the TMC is update we ALSO will update the AUDIT file. The order of the enq/deq is to first ENQ/LOCK the TMC, update the TMC, ENQ/LOCK the AUDIT, update the AUDIT, DEQ the AUDIT and finally DEQ the TMC. Now, some tape events (creating a secondary file for example) may cause 4 different updates to the TMC and AUDIT. So, creating many (thousands) of secondary-files in a short period of time will cause a LOT of I/O's to the TMC. And if each secondary-file is also cataloged; that will simply increase the number of I/O's and cause delays in the CATALOG address space.
One way to avoid the delay in the CATALOG address space is to run the SMFQ subtask of the CTS address space.
How many systems are sharing the TMC and AUDIT file, and are you converting our RESERVE to a global enqueue using a GRS-STAR or MIM configuration? (GRS-RING should not be used, much to slow.)