How can I measure a specific bottleneck in Gatling before applying optimizations?

Consider a simple Gatling simulation that sends HTTP GET requests to a service endpoint, wrapped in a group named "api-call". Before making any changes to the backend, I want to know whether the latency observed for this group represents a bottleneck that warrants optimization.

Which Gatling metric should I collect to isolate the bottleneck? How can I configure the simulation to report per‑group statistics (e.g., mean, p95) for the "api-call" group? What threshold values can I use to decide that the observed latency constitutes a bottleneck worth optimizing?