If you were running a real business with these would the aim not be to overprovision and to setup auto scaling in such a way that you always have excess capacity?
For scaling N --> N+1 - If you configure the correct concurrency value (the number of parallel requests one instance can handle), Cloud Run will scale up to additional instances when getting to X% (I think it's 70%). That will be before the instance is fully exhausted. So your users should not experience the 19 seconds cold start.