On my homespot we have often in the summer season very low wind conditions (asolutely no wind on the water and probably 4-6 nds at 30 m). if you don't know very well this phenomen you never would try to launch a kite this day; its surrealistic this 'oily' flat water and you flying at 15 to 20 nds on...
i own the chrono 12 and 15 m2 and it seems to me that the 15 m2 is the better choice in ultra lightwind; it flys nearly in the same conditions, the 15 m2 is amazingly fast even with 35 m lines and 65 cm bar (500 cm2 frontwing 9 mm profile 82 kg; 142 clm 48cm wide board) i prefer it clearly to the 12...
I own an Zeeko 21 and 17 m2, also a chrono 15m2: - the chrono 15 works fine in 5 nds (original line lenght, 82kg; high aspect wings prototype foil ; low volume board) it seems to have the same power as the 21 with a range for me 4.5-17 nds (huuuuge jumps). at 10 nds with the 21 I was "overpowered". ...