Multi-Radio Dual Connectivity (MR-DC) is a key 3GPP technology that enables traffic aggregation between two base stations (BSs), and thus, increasing the per-user data rate. However, the schemes for traffic aggregation management of such technology are left up to vendor implementation. In this paper we show the importance of using an efficient traffic aggregation method to increase the throughput performance of both TCP and UDP-based applications in MR-DC operation. Targeting the gap on the state-of-the-art on this topic, we propose a cross-layer low control mechanism, which efficiently aggregates traffic based on the instantaneous available radio resources and buffering delay of both BSs. The aggregation is performed independently of the MR-DC architecture option, MAC scheduler logic, and transport layer protocol in use. By means of exhaustive testbed experiments, we show that the proposed method exceeds the performance of a benchmark and state-of-the-art low control solutions and achieves at least the 85% and 95% of the theoretical aggregate throughput for TCP and UDP traffic expected from the use of MR-DC, respectively.