I don't see how the differential amplifier circuit could be implemented with AD8015, which is no general purpose OP-Amp. It e.g. has no freely connectable non-inverting input.
Regarding input impedance, please consider that the differential amplifier configuration according to the schematic has different input impedances for + and - input, also the impedance of the inverting input depends on the signal applied to the non-inverting input. It's effectively not suited for any kind of impedance matching or applications that require a balanced load, e.g. when amplifying the output signal of a sensor in bridge configuration.