Copayments
If the secondary payer is a federal plan (ie. Medicare, Medicaid, etc.) then I would not collect anything until after both payers have sent you the EOPs (EOBs.)
If the secondary payer is commercial (Aetna, BCBS, Cigna, UHC, etc) then I would collect the $15 copay if the practice wanted us to taken some kind of payment from the patient in the practice's policy on the day of the visit. But our practice policy is that if they patient has dual coverage we do not take anything from the patient until both payers have processed the claims and we have recieved the EOBs showing patient responsibility. Then we bill the patient if they owe anything.
If they are lucky enough to have a 100% allowable coordination plan then the seconday will pay the patient responsiblity from the primary plan. If they have the "other coordination plan" (was at one time called maintenance of benefits), that has changed names more than I can keep up with, then they will be responsible for at least the $15 copay.