how much can a quarter horse carryy

we have a 15.2 hand 9 yr old quarter horse that is on the stocky side i am not sure of his weight but he is not under weight or ill in any way shape or form. i wanted to know how much he can carry. my weight is 200 lbs and my daughters is 116 lbs. we wanted to know if he could carry us both so that we can take quiet walks around on the farm with him bare back. the ground is mostly flat. can he carry us both ocassionaly and have no harmful results.