The interview process, for me, took about 3 weeks. The last two weeks I had an interview almost every day, about 8 interviews in total over 10 business days. The order/people I interviewed with basically followed this model: recruiter, hiring manager (x2), area VP (x3), regional VP (x2), and another area VP. Most of the interviews were with a single person, but one ("the challenge") was with most of the listed personas. Throughout the whole process both the hiring manager and area VP were calling to give feedback, which was incredibly helpful; they showed their support to me as a candidate, coached me a bit, and gave great insight into the area/company culture. Truth be told, I felt like I had already been hired on given the amount of MongoDB prep I was doing, and the daily feedback I was getting.
Briefly, I want to cover the challenge: "the challenge" is basically a QBR that you're doing for MongoDB before you get the job. It's the last interview, the make or break. You're researching accounts, ranking them, picking personas, hypothetical targets, writing hypothetical emails, and defending your theory for why/how you did all of the above. It's definitely a well-thought out culture/experience, so over-prepare for this piece. On top of that, you'll be presenting a MongoDB slide deck too. While the slide deck is mostly standard now, with all of that stuff combined it becomes overwhelming. One tip: learn the MongoDB lingo for this. It's a very strong culture, and as a result, knowing the lingo goes a long way.
Overall, it was a process that was true to how MongoDB does things. You'll definitely find out if it's a fit for you going through it. It could have been less stressful... and yes, I'd say it was above average even for an interview process, but most of that would have been alleviated if it had been a week longer.