Next generation mobile networks will offer high data rates to users utilizing new radio access technologies. In addition, new applications as well as devices such as smartphones and tablets will result in a rapid mobile traffic growth. Consequently, a rapid increase of the load in the mobile backhaul segment is expected, resulting in turn into a substantial increase of the energy consumption. An optical mobile backhaul network is proposed as the suitable solution to transport the mobile user data in an energy efficient fashion while ensuring a low latency. We propose in this paper to evaluate, analytically and by simulation, the latency in such next generation optical mobile backhaul network for realistic scenarios. The impact of class of service handling is also quantified.