[DO NOT MERGE] Bump version number from 2.3.14 to 2.3.15

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.android.dialer"

    coreApp="true"

    android:versionCode="20314"

    android:versionName="2.3.14">

    android:versionCode="20315"

    android:versionName="2.3.15">

    <uses-sdk

        android:minSdkVersion="23"