18% is a serious gradient. People who have never ridden this steep probably dont realize just how steep. When I am touring, I class 18% as a gut-busting ordeal, whereas 14% is merely hard.
Fit some lower gears. You may be able to shed a small amount of weight but that wont help a lot.
The options are:
Larger rear sprockets with an MTB rear mech.
Smaller chainrings using an MTB style chainset.
You may have to change your derailleurs to MTB style to cope and you may have to change your shifters to be compatible with the mech.