My family of 4 flew that same route in PE in November of 2019. It was as comfortable as a 17 hour flight can be without being in business. Not sure if the flight times are the same, but we chose the LAX departure instead of the Seattle flight because it left at night, meaning we would be tired enough to sleep. I think I got about 6 hours, which is great for me. We were in the middle 4 seats and it was fine since we are family and the kids were still small. Food was great and so was the service. I would say it was the best PE experience I've ever had, but still not anywhere near business with a lie-flat seat. (Not that you asked, but Condor was the worst PE)
I suggest you watch videos on YouTube so you can see what it is really like.