I agree, the idea to HCG is to stimulate production of LH ( lutenizing hormone). This will in turn allow the testes to produce testosterone. Now if you are in Doctor prescribed hRT that means your body does not produce nearly enough endogenous hormone. That being said he is prescribing exogenous testorone to combat this deficiency.
You doctor does not know what he is doing sorry to tell you.
My recco
Run your prescribed meds. HCG is only benificial to run to jump start the testes in a normal functioning male.
However I am not sure how long he will keep you on test. At somepoint you will need to take HCG to produce whatever endogenous test you can, or you will shock your body, crash and have testicular atrophy for a good month or two.