Hello Saurabh
As far as optimisation goes (number of work processes etc.) it is best to discuss with your Basis team. I can tell you that this report, as a general comment, runs very inefficiently - firstly since it includes all objects in Item D table and, as with lots of other standard PPM code, triggers lots of other processes/calls/methods that may not all be applicable. Hence you may find that the 40/45 second gap that you experiencing might be due to some other stuff finishing off. If you do a SM66 trace you will see lots of things happening, and also depending on your configuration this process may take longer - e.g. do you have financial views configured as integrated and also rolls up to Buckets.
I am not quite getting what you mean with the 12 jobs and 3 variants paragraph?
Regards
C