Do you have adequate gearing on your road bike? What a loaded question!!!
I have a 32/29 as my "easiest" gear. Some people with touring triples have even easier gears. Some, like Road Raven, I believe, only use a double. It ALL depends on you, your terrain and how you want to ride. Sure your "granny gear" on your MTB is easier - your gear ratios are much easier to spin up steep stuff. That's how most MTBs are and, I believe that MTBs were the first bikes to use triples, and then road riders and manufacturers started seeing some of the benefits of these easier gears. (If this is wrong, SK will correct me!)
But the question is what works for YOU. And none of use can really answer that. Can you get up the hills you want to get up? Does it hurt your knees? Do you find yourself having to stop during hill climbing? Do you have to walk?
You are probably fine with the gears you have, but if you answer those questions yes, then you might want to think about a cassette with a larger cog in the rear. That's the easiest and quickest way to get yourself some easier gears.