A Unity 2017.3 app takes ~2.5 seconds longer to load than a Unity 5.4 app on RS4 (Time spent in UnityPlayer.dll!Export...New functions)

I think I got, it is in the Initialize Graphics thread calls, there is about a ~12000 ms slow down, were ~6000ms of time is unaccounted for by our profiler and the VS profiler.

It looks like it is happening when we are trying to read objects aysnc in the loading manager, there is a File.Open followed by 2 reads. Everything is kind of pointing there at the moment. I post what I got, but I need to code in more profiler data to get a better understanding of what is happening.

Notes:
RS4 - 17107.1000
Found the load time added when upgrading a project is 2.340 seconds
performance profile samples

Tests
2017.3 VR = repro
5.6 VR = no repro

2017.3 Non VR = repro
5.6 Non VR = no repro

Favro card
https://favro.com/card/c564ede4ed3337f7b17986b6/Uni-39236

Repro Steps:
1.) Open a project in 2017.2
2.) Setup in the project for Windows MR
3.) Enable the profiler to auto connect to the app in the build settings
4.) Build the app
5.) Open the Profiler in unity
6.) Launch app to the MR HMD
7.) Watch the profiler
8.) Observe at start of the splash screen and the first scene the cpu spikes
9.) Check the Call tree when the spikes occur

Actual:
I think I got, it is in the Initialize Graphics thread calls, there is about a ~12000 ms slow down, were ~6000ms of time is unaccounted for by our profiler and the VS profiler.