Ive got my campag bike up a 31%, its no different from sram or shimano with respect to ratios. You have a few options;
cheapest get fitter/ perhaps lose weight (it can get up things with work);
or fit the largest cassette you can without needing a new derailleur (I guess something like 12-27 or 13-28); that'll make easier without costing too much;
or fit a larger mtb cassette but you'll need a mtb deraileur but it'll make thing even easier;
or fit a compact chainrings (not as effective as cassette changes);
or fit compact chainrings and a 12-27;
or go the whole hog (most costly) change the chainring and a mtb cassette;