Cracked open our 2015 today (lots of pics)

While you have the intake off, it is easy and inexpensive to replace the PCV valve.
You could consider an oil catch can to help stop a lot of that oil from getting to your intake.
I had great results cleaning my egr cooler with oven cleaner, suggested by @ASRDogman

 

All those valves look clean! Mine where nasty!
With all the highway driving it will likely be a long time before head gasket time.
I went 301,000 miles before mine went. 85% of my driving is highway mileage.

Usually the knocking in the mornings is from it being hot when you park and it's cooler outside
so you get the condensation. I got it 2 days in a row, but my coolant level is just below where
I set it. I knew it would go down slightly after driving it some but it's leveled off and has been steady.

Like Khezekiah said, change the pcv valve, it's $10, and get a Toyota one. And replace all the gaskets!
It's really not worth the risk of using the old ones and have a possible leak. All together they are about
$20-30.

 

+1 - although I was chastised for mentioning the oven cleaner instead of something like Simple Green.
YMMV

Consider lowering your OCI to 5K, and ++ on the Oil Catch Can.

 

Don't forget changing the ICE coolant. There is some who believe that degraded coolant affects the rubber in the head gasket adversely.

 

It's tricky getting usable pictures of the EGR cooler interior;you need to override auto exposure. Anyway tried bumping it up; looks to have been quite occluded, for significant time. That would mean restricted flow, and cooling ability.



Doesn't hurt to be optimistic about the head gasket, but I wouldn't start the party just yet: research sources for the gasket kit, head bolts and the double-hex driver. Some info in my signature (on a phone turn it landscape to see signatures). Check the engine coolant reservoir level frequently, too.

 

DANG!
If you can get this car from getting Wisconsin-winter skin and bone cancer, you might have a half million mile car!!

The only thing I didn't see is where you bore-scoped the cylinders.
The one advantage to the car being "dealer maintained" is that they likely used OEM plugs if you had them changed on schedule - which means (I think) you're good to 240 for those.

 

Have you opened the valve to check for a rut through the rotor-stop "ski jump"? You want no sign of a rut.

This one shows the start of a rut:

 

Before you spray it on, make sure you clean off all the dirt and grim.
Or you'll be inviting rust...

As of right now it actually looks really good underneath with minimal rust for wisconsin standards. This summer I think I'm going to apply something like that rust bonding paint to any steel underneath. Im hoping we can at least double the miles on it.

 

A couple of times I’ve “addressed” the underside of our ‘10. One weekend I’ll raise one end; another weekend the other, break it up. The rear seems most rust-prone, due to kicked up road salt I think. I’ll raise and safety-stand one end, take off wheels, leaf-blow and brush any grit or loose rust. Remove some of the plastic “protection” panels. Then I applied boiled linseed oil, with foam brushes, rags, tooth brushes. Any bolts/screws removed I’ll soak with oil before reinstalling.

Prius rust what’s your experience ? | PriusChat