hey sis, u dont need a car seat, i dont have a child yet but the last two time i been on PIA i see people with 3+ kids and no car seats, but u do have to get ur baby a seat of his own, u cant keep him in ur arm for 15 hours, he will be uncomfortable n u will be twice as mad.....
he can sleep in the seat next to you and has a seat belt which is safe and i think u should ask PIA people.
Good luck, im sure ur hubby is excited to see his son n vis versa
All planes are loud, u might have to bear it for the first two hours n then its okay everyone jus sleeps, but make sure u dont sleep cuz ur son might fall on the floor, the people i seen on PIA with kids dont gave ... bout their kids n let them walk n run around lol....
have a blasted trip n insha'allah till then may Allah SWT give u good news