I have a large rails app that was plagued with slow specs using factory_bot. Associations in factories are especially dangerous given how easy it is to build up big dependency chains. The single largest speedup was noting that nearly every test was in the context of a user and org, and creating a default_user and default_org fixture.
there's a profiler that can show you what to focus on, probably fprof here: https://test-prof.evilmartians.io/ (been a while and I don't remember exactly what I used)
(now maybe that's what you used to see what was causing the slowdown, but mentioning to for others to help them identify the bottlenecks.)
Finance users had changed in the meantime, so I navigate and create an iam user, ok, billing administrator is a thing, great.
Oh, they said it didn't work? alright, there seems to be a project billing administrator as well as an organisation billing administrator? weird, ok let's try that.
Hmm... it still didn't work? let's look around a little more. Ok, within the billing account (that they're a billing administrator to) and within the organisation (that they're a billing administrator to) there is a tab called "payment users". This seems to be _separate_ from their IAM users, and the person needs to be added there (as well as? instead of? who knows) and _then_ they can change the card details.
UX is especially crap here (for google cloud billing).
Let's not even get started on the whole vertex vs. aistudio stuff. Also when one of the gemini's came out their python library worked while their curl docs, and their ruby client didn't so we had to read the source of the python library to figure out what it actually did under the hood to test it out. (this was a while ago, I think they might've gotten better since but the documentation/devex was really bad at at the time)