How do I connect to my Epson workforce 615?

Your printer does not appear on the AirPrint supported printer list found here.

http://support.apple.com/kb/ht4356

So you will nee a third party printer app. Print Central, Print Bureau, Print and Share and other apps are available that claim to work with virtually any WiFi printer. You can search for more in the App Store.

You can use your computer as the print server by using apps like Print Magic for Windows or Printopia for Mac so you can check those options out as well.