Although much research work has focused on identifying different factors that affect presence, it is still not clear how to effectively combine these results to create a content with high presence with respect to a given hardware set-up and limited computing resources. This paper proposes a concept of level of presence (LOP) in which we attempt to select a set of presence elements and their levels to maximize their “contribution” toward the overall presence subject to system resources. Such an optimization scheme would require a reasonable characterization of the computational costs and a sufficient knowledge of the relative and collective merits of various presence elements. We made an attempt to apply the LOP concept to VR system design for a particular application, a virtual fish tank. The purpose of this study is to assess the usefulness of the LOP concept and introduce science into content creation. We selected two important presence elements—the field of view (FOV) and the simulation level of detail (SLOD)—and quantified their costs in terms of the required computation time. Next, we ran a simple experiment to quantify the relative benefits of those two presence factors. For this application, it was found that providing more lifelike simulation, for instance, incurred needlessly expensive computations compared to the amount of increased benefits. Based on the result, the virtual fish tank was configured with the appropriate FOV and SLOD for maximum presence under different conditions, such as the preferred frame rate and total number of objects. We discuss the merits of such a presence-driven VR system development approach.