Do we need a separate porta potty for the catering staff?

You do not need a separate porta potty for catering staff if the guest bank already covers the headcount. A dedicated unit near the tent is still worth it for speed and guest experience.

With 150 guests plus 15 staff and an open bar, people leave the guest cluster more often. Your eight standard units and one ADA-compliant unit near parking already give guests a solid bank. Staff walking 100 feet every break still works, but it pulls cooks and runners away from service during the busiest stretch.

What I have done on similar dinners is drop one extra standard unit behind the tent for crew only. Guests never see it, the guest bank stays cleaner, and the caterers stop cutting through the reception line. Label it Staff or put it behind a barrier so guests do not wander in.

If your quote is tight and you cannot add a unit, keep the shared bank and ask catering to use it during setup and teardown when guests are not in line. Mid-event, that 100 foot walk is the real friction, not a rule that says staff need their own toilet.

Yes, add a dedicated standard unit for the catering staff. Megan is right about the convenience, but she missed the health department rule for food service workers. Health department rules often require a separate handwash station for food handlers, and a dedicated toilet prevents cross-contamination from the public area to the food prep zone. Your 15 catering staff also trigger the OSHA 1910.141 general industry standard, which requires two toilets for that employee count. The guest bank covers the guests, but the staff need their own facility. Place the unit near the catering tent with a handwash station. This setup keeps the guest cluster cleaner and satisfies the health inspection requirement.