To use C++17 syntax(e.g. if with init statement), intelliSense needs /std:c++17 option to work properly.
Also, it seems /Yu option helps intelliSense performance.
Not a bit deal - but, when using source control, i have to generate project files every time and modify opetions again.
It will be very convenient, I guess.
Two years later, no answer?
I have found CppStandard (CppStandardVersion) in this document:
Also, the versions can be found with a bit of searching:
https://github.com/EpicGames/UnrealEngine/search?p=2&q=CppStandardVersion&type=
There’s a PCHUsage (PCHUsageMode) property, however, I’ve been less successful in finding the variants of this and how they relate to having to add /Yu to the NMake Additional Options parameter in the project file to make intellisense fast again.