Latency got worse right after a deploy: what do you do?

A new version went out and 10 to 15 minutes later latency or reliability is degrading. Explain how you would notice, how you decide whether to roll back right away or investigate first, how you measure the impact on customers, and what you change afterwards so it does not happen again (canaries, staged rollout, alerts, post-incident review). Treat the timing as a lead to check, not proof.