I suppose I might not be the best one to answer this question, as I didn't really have too much body hair to start with... just a light covering of coarse dark hair, and not a huge amount of arm or leg hair...
But let me tell you, for me HRT almost COMPLETELY knocked the stuff out. I'm talking at least 70% reduction. A significant portion of it went back to being those soft transparent blond vellus hairs that I used to have as a kid, and the hairs that remain have gotten MUCH thinner and lighter in color. After only 3 months, it's already reached the point where I don't ever have to shave my arms anymore, only need to do my legs every week or two, and hell, I haven't shaved my body hair in over 3 weeks now and I still pretty much can't even see it when I'm looking in the mirror anymore.
Before HRT, I could never shave my chest hair, because it was so coarse that every single time I did it, I would get TERRIBLE razor bumps all over. The best I could do was cut it down with a pair of trimmers and shave it VERY carefully with the grain. Well, now I don't have to anymore. It's gotten so much lighter and thinner that I can just whip out the razor, shave it completely against the grain with no anti-razor-bump precautions whatsoever, and it's completely fine. So yeah. The thickness has gone WAY down.
I'm not saying that everyone will get these results. Some get lots of reduction, some get almost none. I got a lot. It is possible.