Those readings are generally the "effective" range for acceptable lure weights. So, if your rod has a maximum recommended weight of 1.5 oz. and you throw a 2 oz., you are simply going to see some loss of effectiveness the farther away in weight you get from the top (or bottom) end range(s).
We all experience the same thing at the other end: a rod unable to handle a very light lure, one that is below its minimum. It is very frustrating to use over-powered equipment on light tackle.
Sure, you could break a rod tip if you do something really silly but remember in the end, your goal is to have a 5 pound plus bass yanking on the end of your line, you yanking on the other, so that is considerably more dead weight and total force than 2 oz. - - - 5 lbs. is 80 ounces on one end and your strength and weight yanking on the other. If a rod can't handle 2 ounces, they'd break constantly from hook sets on large fish.
Force will play a factor here and the slinging motion of a hard cast magnifies the effects of a 2 oz. casted lure so it isn't "linear" here.
My guess? You won't be very happy throwing an over-weighted lure just like you wouldn't be happy throwing an extremely light lure on a heavy bait casting rod. Nothing feels worse than casting an over-weighted lure and then the sluggish feel of reeling it back up. You will feel the under-power very clearly