Getting to the round and true state quickly shouldn't be a concern, and is usually a sign that good quality components were used. The problem with low tension is that it leads to broken spokes, due to the repeated flexing at the spoke elbow. But the spokes have to be quite loose for this to happen. If you're still concerned, find a known, good wheel with similar design (spoke count, gauge, etc.) and give a few spokes some small adjustments with your spoke wrench. If the effort needed to turn the spokes is similar to the effort on the wheel you built, you should be ok.