Add known issue docs for #111854 (#111978)

docs/reference/api-conventions.asciidoc

@@ -334,6 +334,7 @@ All REST API parameters (both request parameters and JSON body) support
 providing boolean "false" as the value `false` and boolean "true" as the
 value `true`. All other values will raise an error.
 
+[[api-conventions-number-values]]
 [discrete]
 === Number Values
 

docs/reference/release-notes/8.15.0.asciidoc

@@ -22,6 +22,10 @@ Either downgrade to an earlier version, upgrade to 8.15.1, or else follow the
 recommendation in the manual to entirely disable swap instead of using the
 memory lock feature (issue: {es-issue}111847[#111847])
 
+* The `took` field of the response to the <<docs-bulk>> API is incorrect and may be rather large. Clients which
+<<api-conventions-number-values,incorrectly>> assume that this value will be within a particular range (e.g. that it fits into a 32-bit
+signed integer) may encounter errors (issue: {es-issue}111854[#111854])
+
 [[breaking-8.15.0]]
 [float]
 === Breaking changes