Researchers have sought solutions to interconnect different radio access technologies, enabling them to coexist in the current and future heterogeneous network environments to obtain additional benefits. This paper presents SVORA, an innovative approach that integrates the concept of Virtualised/Open (V/O)-Radio Access Network (RAN) with a Service-Based Architecture (SBA) in order to optimize the energy consumed by the network and minimize the communication delay. In the context of SVORA, the Delay-aware Energy Efficiencybased RAN selection algorithm (DEER) is proposed. DEER employs utility functions and considers Quality of Service (QoS) metrics such as throughput, resource block utilization, delay, and energy consumption measurements when finding the RAN to best support the requested service. DEER is highly flexible, being able to be tuned to support critical delay services, prioritizes energy saving, or observe a balanced approach. Testing shows that the SVORA-based DEER was able to increase the number of users and the aggregate data rate by about 10%, whereas the delay and energy consumption decreased by approximately 90% and 50%, respectively.