Most modern 18m were optimized for 18m, but but can fly well as 15m. The only weakness of the 18m in 15m is they are heavy. Most are 100 to 150 pounds heavier than a pure 15m glider. The 29 does well in locations with stronger conditions, but suffers on very weak days. The motor versions are at a significant disadvantage in lighter lift. On the other side they do better in very strong conditions with significant cloud streets.

It will be interesting to see the next generation of 18m and 15m gliders.

I still prefer a true 15m glider with empty weights at 520 to 560 pounds over the much heavier wings of the 18/15m gliders.