May 3 "Whatever you can do, or dream you can, begin it. Boldness has genius, power and magic in it. --Goethe"
Why would you do more? Like anything we pursue in life strength training has a point of diminishing returns. At some point x in no longer equals y out. Eventually 2x in starts to equal y out, then 3x and 4x in. Think of recovery like a cup. The more volume you add the more the recovery cup empties to get you ready for the next workout. If you have more volume than the recovery cup can handle, you aren't recovered by the time the next workout comes. Life is very busy for the high school athlete. There are numerous demands on their time.
In addition to the normal academic demands, athletes have sport demands. Sport demands can further be broken down into strength training demands. Everything is cumulative. So if you can save some time somewhere, it's a good thing. Time saved can be shifted to be utilized to improve another area the athlete needs improvement in. Also though, time saved can be banked, that is not spending the 20 minutes saved by having them practice 20 minutes longer at something else. This can foster improved recovery both physically and mentally from sport.
The key is to monitor your progress and keep accurate records. From that point if you add more volume you can see if your gains keep up, or slow. Conversely you can reduce volume and if the gains stay the same, then you've got a win on your hands. You can reduce the strength training stimulus while getting the same strength gain. This allows better recovery for the athlete. As stated earlier, don't be quick to spend the reduced volume by filling it with other exercises. Less can and often will be more.
Reduce the sets - An obvious way to reduce the amount of volume. Many studies show one set is enough stimulation for strength and muscle gains and diminishing returns set in on the third and subsequent sets.
Remember, one of the key reasons powerlifters and olympic lifters do many sets is for the practice of the lift itself. Their one and only goal is to lift more weight in that movement. Set upon set helps to build motor memory for that movement and when you are lifting for competition, you want to be able to hit the efficient groove 100% of the time.
Strength training for athletics is not the same. You are trying to make the athletes stronger, but you are not trying to turn them into a world record squatter, so having them squat as a world record pursuing lifter doesn't make sense. It's waaay past the line of diminishing returns.
Reduce the total reps - This one is also an abvious way to reduce volume. This one can also cut down on DOMS that your athletes may experience. Delayed onset muscle soreness primarily comes from the eccentric phase of the movement and the more reps that are done, the more eccentric contractions.
I'm not saying go to heavy singles, but you can cycle in some lower rep sets from time to time. What I'm really saying is reduce the reps by reducing the sets and NOT changing the amount of reps in your existing sets. Go from 3x10 to 2x10, not 2x15.
Fewer Exercises - Look at decreasing assistance work on some of the prime movements, but also consider reducing the prime movements temporarily and focussing more on the assistance movements. Many times the assistance work is not done with enough intensity as it's an after thought to the prime work. As such the assistance work doesn't reach the intensity level required to stimulate optimal gains.
Consider dropping prime movements one week of every four. This will allow more intensity on the assistance work and allow the prime movers to get some much needed rest. I think you'll find the benefit of doing so. Just be sure not to add more assistance work that week. You may work to up the intensity of what is in place, but don't add more exercises or you'll defeat the purpose.
If you look around at what you are doing you will find places and ways to save time and wear in your strength training program. This is also an activity where another set of eyes can help. Talk to other strength coaches and agree to critiqe each others programs with an eye toward reducing the work. That other coach will probably spot ways that don't occur to you and vice versa.