Wow, Python startup time is worse than I thought. Here’s some data from a fast Ubuntu box. I ran all commands a bunch of times to warm caches.
That last one’s a bit of a winner; -S means “don’t load site modules” and comes from this ExpertsExchange discussion. I lose /usr/local/lib; if I manually add that in my script I get my minimal libgit2 program down to 6ms.