k8s: Bump k8s version check interval to 15 minutes
k8s: Bump k8s version check interval to 15 minutes

At 1k nodes, a 5 minute interval still leads to 3.33 apiserver interactions per
second. The health is primarily determined when the last event has been received
so we can be more conservative in forcing a full version check.

Signed-off-by: Thomas Graf <5f50a84c1fa3bcff146405017f36aec1a10a9e38@cilium.io>

tklauser/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium-team/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium,cilium-team/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium