Heterogeneous networks (hetnets) is an interconnection of distinctive networking paradigms to enable wider reachability and greater collaborations. In large Internet-of-Things (IoT) applications, many wireless networks are spatially co-located and intertwined forming hetnets; for instance, health monitoring devices utilising ZigBee or IEEE 802.15.4 co-exist in 2.4 GHz spectrum alongside Wi-Fi devices. Interoperability or non-obtrusive operations are required among the disjoint domains to achieve operational efficiency in overall IoT ecosystem. Specifically, network interoperability in hetnets assure desired reachability, resource orchestration and network quality. In this work, we have modelled and implemented a simulation environment for hetnets to support different schemes of network interoperability under distributed and centralised management of network. The implementation has been evaluated for network scalability and reliability to replicate large IoT hetnets. By evaluating against increasing number of nodes in the hetnet, the mean latency under distributed management is improved by 100-fold with the centralised management. Similar observations could also be made for throughput and packet loss rate.