Most folks don't realize how stragly and spindly, and lacking for good branching they can get without regular pruning at least once a year, and I'd prune mine dormant down to just a few old leaf nodes on last years growth each spring, for sturdier , but fewer branches, than a longer pruning would provide. Without any pruning they might just resume growth on the previous years branch tips each spring with little or no new branches year after year. Depends also on whether you're looking to train as a single stemmed "standard" or a shrubby multistemmed specimen as well. They can get very tall, but serious pruning each spring can keep them down to size.

So as not to over-do-it, try the 1/3 process of pruning. Prune back 1/3 of the limbs by 1/3 of the length. Let them grow next spring and when they have sprouted new limbs, cut another 1/3 of the limbs back by 1/3. You can accomplish this with ROS in one season and get it back into shape.