Update agents.mdx (#664)

docs/agents.mdx

@@ -29,6 +29,6 @@ agent behavior:
 - `language` sets the agent language (for more context see [Multilingual Agents](/multilingual))
 - `initial_message` controls the agents first utterance.
 - `initial_message_delay` adds a delay to the initial message from when the call begins
-- `ask_if_human_present_on_idle` allows the agent to speak when there is more than 4s of silence on the call
+- `ask_if_human_present_on_idle` allows the agent to speak when there is more than 15s of silence on the call
 - `llm_temperature` controls the behavior of the underlying language model. Values can range from 0 to 1, with higher
   values leading to more diverse and creative results. Lower values generate more consistent outputs.