Updates deprecation notice of v1 UI (quay#1376)

Co-authored-by: Steven Smith <[email protected]>

Author: stevsmit

modules/rn_3_15_0.adoc

@@ -158,7 +158,7 @@ There is a known issue affecting the mirroring feature of {productname}. When th
 [id="deprecations-315"]
 == Future deprecations
 
-* The {productname} v1 UI will be officially deprecated in a future release of {productname}.
+* The {productname} v1 UI will be deprecated in {productname} 3.16.
 
 [id="bug-fixes-315"]
 == {productname} bug fixes