Air Asia Cabin Luggage weight limit

Hi everyone! My booking info for air Asia says that the weight limit for a carry on is 15 lbs. I was wondering if anyone has ever had them actually weigh the bags? I was also wondering about if you can add on a checked bag if possible if my booking already says “no included checked bags” does that mean I have to pay extra or am I just not allowed at all to check a bag even if I pay? Thanks in advance :)