Hi Amal,
The number of iterations will depend on efficiency, skill, management and engagement of business , technical and end user teams involved.
If you have done projects based on Agile methodology, you can draw an analogy with that.
I would suggest invest time and efforts first time and set up an UX Centre of Excellence (COE) and UX strategy. All subsequent projects can leverage that and cut down on number of iterations.
Thanks,
Indrajit