Yes, in tune with the most of the phones being made available these days, you do have the USB OTG functionality on the Samsung Galaxy J5. You can connect your external hard drives to the phone and the view the files stored on those drives on your device. Please note that the file system compatibility between your phone and that on the external drives. If the file format system on your drive is not supported by the phone, you may have to format your external drive to the supported format. Kindly ensure that you have backed up the data before doing so.
Also, it should be noted that the sales package does not include USB OTG cable. You will need to buy it as a separate accessory. Also note that the USB Cable provided with the device cannot be used for the purpose of OTG. USB OTG refers to using your phone as a host to view the file on source drives, while USB cable will let you view the content on your phone on a host like a PC or laptop.
Live....and Let Live!