Between 11+14 and 11+15, in calls to bootstrap this:

    public static <T> Comparator<T> comparingInt(ToIntFunction<? super T> keyExtractor) {
        Objects.requireNonNull(keyExtractor);
        return (Comparator<T> & Serializable)
            (c1, c2) -> Integer.compare(keyExtractor.applyAsInt(c1), keyExtractor.applyAsInt(c2));
    }

... the parameters to altMetafactory for the indy has changed:

11+14:

  3: #159 REF_invokeStatic java/lang/invoke/LambdaMetafactory.altMetafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
    Method arguments:
      #160 (Ljava/lang/Object;Ljava/lang/Object;)I
      #185 REF_invokeStatic java/util/Comparator.lambda$comparingInt$7b0bb60$1:(Ljava/util/function/ToIntFunction;Ljava/lang/Object;Ljava/lang/Object;)I
      #160 (Ljava/lang/Object;Ljava/lang/Object;)I
      #162 5
      #163 0

11+15:

  3: #159 REF_invokeStatic java/lang/invoke/LambdaMetafactory.altMetafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
    Method arguments:
      #160 (Ljava/lang/Object;Ljava/lang/Object;)I
      #186 REF_invokeStatic java/util/Comparator.lambda$comparingInt$7b0bb60$1:(Ljava/util/function/ToIntFunction;Ljava/lang/Object;Ljava/lang/Object;)I
      #160 (Ljava/lang/Object;Ljava/lang/Object;)I
      #162 7
      #163 1
      #5 java/util/Comparator
      #164 0

Since the target type is java/util/Comparator, this change in behavior seems to be incorrect