Due to the limited resources of DTMSN (Delay Tolerant Mobile Sensor Networks), network congestion becomes a critical problem to resolve. Traditional congestion control methods where the number of copies is restricted to limit data packet forwarding cannot adapt to constantly changing network environment because of fixed number of copies. Fortunately, this problem can be solved through a real-time algorithm by modifying data packet forwarding conditions. However, one of the major challenges of this algorithm is detecting characteristics of the network environment accurately and efficiently. In this paper, an optimized routing algorithm, RVNS (Reduced Variable Neighborhood Search)-based Spray and Wait (SW) is proposed. In this algorithm, nodes will transmit and store the counter record of each other when they meet, based on which, RVNS is introduced to calculate a real-time threshold for the forwarding condition to control packet delivery. Simulation results show that the proposed algorithm increases delivery probability and dramatically reduces the overhead ratio. In some extreme cases, this algorithm can reach an extremely low overhead ratio (ten times lower than that of SW), meaning that the proposed algorithm suits challenged networks well.