Apple removed Sync Services altogether in OS X 10.9 (Mavericks) and it’s not coming back. This is what Outlook for Mac and Entourage were using. Outlook 15 no longer includes that feature since its minimum OS requirement is Mavericks.
That means Outlook 15 now only supports syncing calendars and contacts using Exchange and Office 365. Exchange Online (Microsoft’s hosted Exchange service under Office 365) is about $48/year and has been rock solid syncing all my data from desktop to mobile device. If you’re interested in moving your account to an Exchange service then I can highly recommend it.
Hope this helps!