The kind of military they have , they can't afford to decrease there defence budget by a big margin , look at their airforce only they are operating the most expensive aircrafts on the face of this earth , billions are spend just to maintain their fleet in the lights of B-2, F-22 raptor etc etc Reducing their defence budget means not only reducing their current military inventory but also holding on current running projects which are too many currently. They have done so with few projects but they can't afford to hold all of them .
The more simpler way for them to pay their debt is evacuate Afghanistan and Iraq by doing so they will get rid of billions of dollars being spend on wars which have no end or result ,They should hand over the countries and other headaches to the respective militaries, that will be more rational