Microsoft have announced that from January 2016 only the latest version of Internet Explorer for that OS will be supported, see Microsoft Support Lifecycle (Internet Explorer) for details.
Sometimes with "Enterprise" deployments of Windows there are issues getting legacy internal sites working with newer browsers. In Windows 10, Microsoft released Microsoft Edge, their new browser, which is great for modern stuff but they also shipped Internet Explorer 11 knowing that many businesses would still need it. This combination is documented in How Microsoft Edge and Internet Explorer 11 on Windows 10 work better together in the Enterprise | Microsoft Edge Dev Blog. This links to a useful article at Use Enterprise Mode to improve compatibility (Windows) which covers using this Enterprise Mode.