btw i recommend getting a laptop between 12"-13" in size. i find that 15" laptops are too big to carry around and have to squint my eyes for screens less than 12". also something less than 3kg would be ideal unless you don't mind slugging around a brick to class (exaggerating). just my opinion
Some of the really low profile 15in laptops are actually not too bad! You pay for it though; the new 15 inch MacBook Pros or Dell's XPS 15 are the two I immediately think of, both nearly $4k (nuts)...
But on the weight, I had a laptop that weighed about 2.5kg for Year 12, I didn't bring it every day but when I did, far out did I notice. I kept that laptop for about 10 minutes walking around a massive UNSW campus and I'm like, "Nup, no way." Bought a refurbished MacBook Air that weighs little over a kilo, far out, best thing I ever did.
There was a period in Year 12 where I flat couldn't use my backpack because I was having back problems because of the weight of the thing. A laptop doesn't feel heavy until you stick it with a bunch of textbooks pulling down on your spine

so definitely go as light as you can without compromising the features you want! If the Chromebooks are your go you shouldn't have much problem there