First of all you are making an illogical comparison with US and China.US completes 9000 ton destroyer in 3 years from laid to passing sea trial. (China is even faster)
Iran takes 5 years to make a 1500 ton frigate.
Can you explain why?
According to this question we have already answered in the past.
But in repeating:
Iran has no problem producing hulls and superstructures for military vessels quickly;
the problem of delays is connected to the fact that military ships are not only made of welded metal plates, to make them operational you need thousands of other components that Iran must produce almost 100% at home, engines, generators, propellers, electronics , artillery armament, missiles etc,etc.
Then it is necessary to remember that the military naval shipbuilding for units that can ply the blue waters in Iran is recent, and as such it has had the need to learn how to build, but also to modify the basic project due to the operational experience with the first two units and the due changes in the supply of components, from propulsion engines, to the evolution in the production in Iran of electronics, radar, armament, etc. but which in any case are not a mass production, but a production which for many components can be defined as artisanal because it is dedicated solely to these Iranian ships.
Therefore it is useless to make comparisons with the naval production of 2 world superpowers, but not even with the manufacturing speed of other nations because often their ships built in their shipyards are filled with components purchased from foreign suppliers, components that often need the intervention of the parent company to be repaired or, for example, for the electronics to be updated (Venezuela docet)