Bumped calico version to 3.15

Bumped calico version to 3.15

Author: kubealex

docs/book/src/user/quick-start.md

@@ -574,7 +574,7 @@ Calico is used here as an example.
 
 ```bash
 kubectl --kubeconfig=./capi-quickstart.kubeconfig \
-  apply -f https://docs.projectcalico.org/v3.12/manifests/calico.yaml
+  apply -f https://docs.projectcalico.org/v3.15/manifests/calico.yaml
 ```
 
 After a short while, our nodes should be running and in `Ready` state,