Sugar is not just the sweetener in jam. In a traditional preserve it is a major part of the structure and of what keeps the jar safe on a shelf.
Sweetness. Figs are already sweet, so fig jam needs less sugar than, say, a sour plum jam to taste balanced. Lemon juice does more for balance than cutting sugar does.
Set. Pectin gels in the presence of sugar and acid. Less sugar generally means a softer set unless a low-sugar pectin is used.
Keeping. High sugar concentration binds water and makes it unavailable to moulds and yeasts. Reduced-sugar jams do not keep as well once opened and must be refrigerated and used more quickly.
Which sugar
Plain white cane sugar gives the cleanest fig flavour and the truest colour. Raw or brown sugars add caramel notes that suit dark figs. Honey can replace part of the sugar but changes both flavour and set.
Reduced-sugar jam
It is possible, and tested recipes for reduced-sugar preserves exist from the sources on our food-safety page. Follow one rather than simply cutting sugar from a standard recipe, especially if you plan to can the jam.