More seriously though, unless he can resolve this problem should he even be flying solo, let alone potentially carrying passengers?
I'd say if this is the first time he has been ill, and it is comes from prolonged stalls, steep turns, recovery from unusual attitiudes etc... (the latter may not be applicable here anyhow), then I think he is OK. I have felt sick (but never been sick) after prolonged exercises, though for me it has been unusual attitude recovery with my head down, but that was for my IMCr and not my PPL. OK one could argue that you dont normally get into these situations, not one after the other for 15 minutes at a time, but if you do, you need to recover but I think the combination of these exercises over a long time is the issue here, and he will be perfectly safe. Not everyone has the stomach for aeros, and many other pilots are safely and competently with or without passengers.