I've had my Brompton for over 4 years, taken it to Europe etc. ... but I really didn't climb anything steeper than the 14% grade to my house until I took a job in Studio City and did an AirBnB (for the week) in the hills off Coldwater Canyon.
Here's my normal daily ride:
And there's an alternate route to the same destination:
The Bike is a H6L (low gear of 29.1") and I am in the Clydesdale Class of riders.

(Guess the City)