A major roll-out of 5G networks is currently underway around the world. In the first instance, users will connect to the 5G network in a non stand-alone mode. This paper presents a study on the optimization of the event B1 threshold for the inter Radio Access Technologies (inter-RAT) connection between LTE and NR technologies in a E-UTRAN New Radio Dual Connectivity (ENDC) scenario. For this purpose, a systemlevel simulator has been used to show the impact of changing the threshold value on the global user throughput and retainability using an File Transfer Protocol (FTP) service in a heterogeneous rural setting.