Did you ever get it to work? When I did it, it appeared "stuck" and 20% and then 60%. It stayed on each said percent perhaps 2-3 minutes each, but it eventually completed. Have you tried with a different cable? All of my cables can be touchy (the lightening connector doesn't seem as robust as the older 30-pin).
So when you start the jailbreak process, your phone has been updated/restored to ios 8.3 and was "set up as new phone"? Meaning, when you start the phone after the restore (not a restore from backup), it takes you through a whole process up setting up a new phone (language, system setup, icloud setup, etc, etc). If not, then you didn't set it up as a new phone.
Setting up as "new phone" is optional. I didn't do this and my jailbreak worked. I've never set up as "new phone" for jailbreaking.
From an 8.1.2 jailbreak, I restored to 8.3 in iTunes. I then restored from backup. Then before syncing, I uninstalled iTunes and reinstalled v12.0.1. I then jailbroke using TaiG 2.1.3 (run as administrator). First attempt failed. I simply tried again and it worked. It paused briefly at 20% and then buzzed thru. Jailbreak took less than a minute...iPhone reboot took another minute. Then synced my apps and media.
I have nearly every tweak reinstalled (except Springtomize) and not a single crash. It's all good.
Edit: naturally, I had Find-My-iPhone turned off and passcode disabled. I also left WiFi "on".