I'm using a lighter materials to rebuild plane, to cut down plane weight to 56kg and a 1.2m 3blades propeller.
With half the horsepower of the original, it will fly, but just barely, even allowing for a bit more thrust efficiency using a larger slower turning propeller. Your airplane may be 15 kg lighter, but the pilot's carcass is as much or more as a share of the total weight.
So figure on maybe, at best, 55 percent of the original's available thrust with a better prop, which like with most light twins, removes probably 70-80% of the thrust available for climb. The original could climb 1300 fpm, so the 15 hp version might manage 300-500 fpm, depending on how hot and high you were and how heavy the pilot is. Gain a little weight from excess beer and your climb margin might disappear completely if the weather is hot and you have a fun 3-wheel go-kart.
In any case, you wouldn't get me in a 15 hp Cri-Cri.