Updated renewal banner timing from 30 to 15 days

doc/subscriptions/gitlab_com/index.md

@@ -71,7 +71,7 @@ The following information is displayed:
 ## Renew GitLab.com subscription
-30 days before a subscription expires, a banner with the subscription expiry date displays for group owners in the GitLab user interface.
+15 days before a subscription expires, a banner with the subscription expiry date displays for group owners in the GitLab user interface.
 Before you renew your GitLab.com subscription, you should [review your account](../self_managed/index.md#review-your-account).

doc/subscriptions/self_managed/index.md

@@ -452,7 +452,7 @@ If you want to renew with fewer seats, you can do either of the following:
 ### Renew subscription manually
-30 days before a subscription expires, a banner with the subscription expiry date displays for
+15 days before a subscription expires, a banner with the subscription expiry date displays for
 administrators in the GitLab user interface.
 You cannot manually renew your subscription more than 15 days before the subscription