the only reasons to go bigger than 15" are for fitting bigger brakes on your car, or because the tire size you want wont come in 15"
also, with bigger wheels, bigger tires are much more expensive, so are you really saving and conserving your money by buying bigger wheels?
in my opinion, big wheels look stupid on our cars unless youve got some big ass stoptechs with 13" rotors or something along those lines
the oem wheels for integras are not light, i have rota slipstreams i picked up for 280$ used in mint condition, and they weigh 12.6lbs per wheel. I plan on buying some enkei rpf1's somewhere down the road, they weigh 9.6lbs per wheel, thats a lightweight cast wheel if there ever was one.
the benefit of having smaller wheels gives you better turn in response, and like someone else said, less rotational mass, your car will have less difficulty getting the car moving