Hi freddie89.
Welcome to our Mattress Forum! 
The recommended durability guidelines are relative to each of the individuals sleeping on the mattress and I’d certainly use the highest BMI of the two sleepers as a baseline (in this case 22 BMI) and not their two BMI’s added together. In either case you both are well within the normal weight ranges and typically the weight is distributed on the entire contact surface quite evenly with some exceptions for people with heavier “areas” or who are more “active” on a mattress that can wear out materials a little faster than lighter, more evenly proportioned, or less active people in which case higher density foams than just the “minimum” guidelines can be more important. I would not have any durability concerns but just in case you wish to rule out some other factors that can affect durability you can peruse post #4 here or post #2 here.
Phoenix