Cutting back my burning bush..

https://www.youtube.com/watch?v=BIT8K6Yxqf0

Cut in the fall (when sap is not running in the bush). When you cut the appropriate branches, they MUST be cut where the particular branch enters the MAIN stock. (do not leave a stub when cutting back)! Hubby was a Tree Surgeon (get it?) for 45 years and I learned from the best! Good luck.

https://www.gardeningknowhow.com/ornamental/shrubs/burning-bush/pruning-burning-bush.htm

where i am located zone 6, you should cut back a burning bush in the mid= spring or early summer since it is a fall blooming bush. you should get rid the died branches which is maybe why you have dead leaves or it could be that you haven't clean up the debris in a couple or more years. this shrub grows like ( wild fire) and can be cut back hard as much you think you want depending how you want to shape it . 15ft. is a large shrub and can be cut down as you feel you want.

https://www.gardeningknowhow.com/ornamental/shrubs/burning-bush/pruning-burning-bush.htm