I moved my tank from my room on the top floor of rez down two flights of stairs, into the van, across town, and then up another flight of stairs into my grandparents house.
I left about 2" of water, all my sand, plants, and decorations in the tank.
My dad helped me carry it, but if an 18 year old girl and a 53 year old man can carry a 15g tank with that much crap in it, it can't be that hard.
I wouldn't worry about the gravel, tbh..