Where did the spokes break? 14/15/14 spokes are just as strong as 14 ga straight gauge spokes IN THE AREAS THAT ARE SUBJECTED TO THE GREATEST STRESSES, the area near the J bend and the area just below the threads. Besides, DB spokes are more compliant than straight gauge and withstand the constant flexing that affects spokes. I believe the lighter the spoke, the more durable it is, even for a Clydesdale. Spokes have plenty of tensile strength. You don't pull them apart, you flex them to death. Use DB spokes. Your wheels will be better.

Also you are not likely to run out of threads before reaching optimum tension. If your still worried, a safeguard would be to add washers at the hub and rim holes. That takes up some slack.