Before our trip I asked our dive company in Ambon what the overwight situation was on departing Wings flights. We were told they do occasionally weigh the carry-on bags too, which is not to say that's practiced system-wide. It's better to not make them part of the equation when you're at the check-in counter, I think.
BTW, our flight was on a turbo, not a jet, and the allowance was 10kg checked and 5kg carry-on, not 15kg and 7kg.
You could be right. Just read the small print and we are booked with Lion air but fly with Wings Air....Bugger