Incrementing VERSION to 115.0.5790.15

Change-Id: Idcee22cbedb881f4ef2ea87fca0fcc2107216812
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4581788
Bot-Commit: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/5790@{#244}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

chrome/VERSION

@@ -1,4 +1,4 @@
 MAJOR=115
 MINOR=0
 BUILD=5790
-PATCH=14
+PATCH=15