Volume of training is defined by 3 things:
Too Often people spend too much anxiety just worrying about duration. Ask just about any athlete how well training is going, they will almost ALWAYS respond with this metric.
The irony, it’s probably the single worst indicator of success, UNLESS you are trying a distance for the first time. It doesn’t matter how fast you can go, if you cannot complete the distance.
If you are short on time, bump the intensity, and shorten the total workout. If you are training for a half marathon for example, as your coach for equivalent 5K run paces and change the set.
3 x 15 min @ half marathon goal may not be realistic on a particular day. However you could do 4 x 6 min @ 5K effort and get a great fitness response, just as an example.
Coming back from injury?
Use frequency. Shorten the duration, not only of the total workout but build in more rest intervals, to include even walk breaks to help build duration and increase overall volume. If you use a muscle 5 min or less for aerobic exercise, it's is a lot less likely to have sustained inflammation.
So 3 x 60 min runs may be a bit aggressive to return. Change it up to 4 x 30 min runs with a day between with 4 min run, 1 min walk.
Too often we get stuck in the ruts we are used to. Changing perspective and ideas can really help!