State Trunk Highway 15 (STH 15, commonly known as Highway 15 or WIS 15) is a state highway running east–west across east-central Wisconsin. The route exists entirely within Outagamie County. Highway 15 provides a "shortcut" to Appleton from U.S. Highway 45 for travelers inbound from points north and west. Most of it was once part of US 45, which was redirected south of New London to bypass Appleton and provide direct access to Oshkosh and points south.