It's less about "big projects" and more about "what features are used". It's entirely possible for a 10kloc project to take much more time to build than a 100kloc project. Proc macros, heavy generic use, and the like will drive compile time way up. It's like comparing a C++ project that is basically "C with classes" vs one that does really heavy template dances.
Notably, serde can drive up compile times a lot, which is why miniserde still exists and gets some use.
Notably, serde can drive up compile times a lot, which is why miniserde still exists and gets some use.