The only time I've had check-in staff weigh my carry-on bag was when I checked in a particularly heavy bag (it was between 25-30kg - can't remember) and she looked at my shoulder bag with worry. Mind you, it wasn't a big bag - it would easily have fit in the overhead bin. In any case, I don't think you'll have an issue with the weight - it's probably more of the size of your carry-ons that will be an issue.