Honestly feel the number is a typo. Mostly due to the size of the guild hall. There are way too few people in any of the images, and the staff too small to service so many people in anything resembling a timely manner.
Think of it this way. To service more then a thousand people in a day the guild hall would need to be the size of your typical big box story like Walmart. Not just because the quest board would be a nightmare to navigate, but they also need to handle quest materials and monster meat and parts, conference rooms, resource library, restaurant, bar, a vault to keep reward payments, training yard, etc, ect...
They might scrape by with under twenty staff is they delt with a few hundred people in a day, but there is no way so few people could provide more then basic quest service to thousands of adventurers in a 10 to 12 hour work day.
Yeah yeah, fantasy bullshit, manga logic, such and so forth. There is no way ten people in a building the size of a Burger King would be able to handle the needs of 1500ish adventurers.