Update minimum Meilisearch version to v1.15.1 for chat feature

Author: tpayet

guides/ai/getting_started_with_chat.mdx

@@ -15,7 +15,7 @@ The chat feature is experimental and must be enabled before use. See [experiment
 ## Prerequisites
 
 Before starting, ensure you have:
-- Meilisearch instance running (v1.11 or later)
+- Meilisearch instance running (v1.15.1 or later)
 - An API key from an LLM provider (OpenAI or Mistral)
 - At least one index with searchable content
 - The chat experimental feature enabled