The combination of recent emerging technologies such as network function virtualization (NFV) and network programmability (SDN) gave birth to the novel Network Slicing paradigm. 5G networks consist of multi-tenant infrastructures capable of offering leased network “slices” to new customers (e.g., vertical industries) enabling a new telecom business model: Slice-as-a-Service (SlaaS). However, as the service demand gets increasingly dense, slice requests congestion may occur leading to undesired waiting periods. This may turn into impatient tenant behaviors that increase potential loss of the business attractiveness to customers. In this paper, we aim to: 1) study the slicing admission control problem by means of a multi-queuing system for heterogeneous tenant requests; 2) derive its statistical behavior model; 3) find out the rational strategy of impatient tenants waiting in queue-based slice admission control systems; 4) prove mathematically and empirically the benefits of allowing infrastructure providers to share its information with the upcoming tenants; and 5) provide a utility model for network slices admission optimization. Our results analyze the capability of the proposed SlaaS system to be approximately Markovian and evaluate its performance as compared to a baseline solution.