The emergence of Internet-of-Things (IoT) has led to the development of new energy efficient and long-range wireless technologies, which are necessary for the successful realization of IoT applications. Within this context, long range (LoRa) has emerged as one of the prominent low power wide area network (LPWAN) technologies that is envisioned to accommodate the future IoT requirements. However, current LoRa frameworks suffer from limited network capacity, particularly in dense deployments. Consequently, power domain-superposition modulation (PD-SPM) is integrated with LoRa to alleviate the aforementioned problem. In this paper, the error rate performance of a LoRa-enabled PD-SPM system is investigated over Rayleigh fading channels. Specifically, symbol error rate (SER) expressions are derived to characterize the performance of an arbitrary number of users under extreme fading conditions. Furthermore, Monte Carlo simulations are presented to validate the analytical framework.