Your data source does not seem to break out teenagers over 15. It does focus on children under five. It has some data just on children, which seems to be under 15 in this dataset but I am not sure and don’t have time to continue to dig in on this. Your dataset is unable to answer the question you are posing as presented.
The vast majority of deaths in countries like Nigeria are young children, old people, and men. Girls and women aged in their teens, which you did not seem to find any specific data for, generally have relatively low mortality. The leading cause of death globally, centered in less developed nations, in this population, is complications from pregnancy. This was until recently generally put down to improvements in western medicine and childbirth being dangerous. Since about 2020 people have started to realize child marriage is the issue.
The reason for this is mechanical: their pelves are underdeveloped and not ready to birth a baby with a big head.
Unsafe abortions is exactly what it sounds like, and a health risk specific to pregnancy. It can be in order to prevent death in childbirth, whether done early and quietly, or during childbirth in more tragic cases.