Application areas like global sensor networks and data stream processing involve the on-line processing of large amounts of data in an overlay network of operators on top of the Internet infrastructure. Trying to fulfill QoS guarantees in such networks is a challenging task that should be realized under the requirement for optimal usage of common resources in the network. Therefore in this paper, we formalize a constrained optimization problem for the placement of operators in an overlay network which strives for satisfying user QoS constraints subject to latency, while minimizing the network load induced by the deployment of the operators in the network. Since the initial problem is NP-hard, we solve at a first step the problem in an intermediate continuous latency space and then we map the continuous solution to its discrete variant. Our evaluations provide an analysis about the inherent interdepedence between the two metrics, network usage and latency, subject to this paper and furthermore shows that our algorithm achieves a good balance between the user requirements and the usage of the network resources.