New growth on Apple tree

We have a small apple tree that was in the garden when we bought the house about 15 years ago. It has been doing well until a couple of years ago when I trimmed some of the branches as they were looking old and crossing but since I have done this it is growing new much longer shoots. Can I trim these back to a couple of buds now or is it best to wait until the leaves have dropped? I am worried that it might be putting all the energy into the new shoots and then exhaust itself!