Kubernetes v1.15.9, v1.16.6, v1.17.2 are now available for any Rancher v2.3+ release.
For any Rancher release that has these minor versions (v1.15, v1.16, v1.17), the latest Kubernetes patch release is available to be deployed.
Note: If you are an air gapped user, please review the documentation on how to get these versions.