Yes, you can set terminationGracePeriodSeconds to more than 15 seconds for non-system Pods on GKE Spot VMs, but it is honored only on a best-effort basis. When a Spot VM is preempted, it gets a 30 seconds termination notice. The kubelet prioritizes gracefully shutting down non-system Pods, usually allowing up to 15 seconds. If you set a longer period like 25 seconds kubelet may attempt to honor it, but system Pods also require time to shut down. If the total exceeds the 30 seconds window, your Pod may be forcefully killed.

Therefore, while values above 15 seconds are allowed, they may reduce the time available for critical system Pods, making 15 seconds or less the safest option for reliable shutdown behavior on Spot VMs. If your workloads require longer shutdown periods such as for draining connections or flushing logs, consider using standard VMs instead.

For best practice you can refer to this documentation for additional information.