I remember reading about misplaced foreign aid back when the impeachment hearings were underway. It may be much more than 1.5b, but the information is not strongly substantiated.
After much searching, (hard to find older stuff given current events), I found this article that touches on suggestions of widespread corruption in handling of foreign aid. That was apparently why Trump was asking them if they had addressed the concerns before he released the additional funds...

https://www.theepochtimes.com/giuliani-alleges-5-3-billion-in-u-s-aid-misused-in-ukraine-u-s-embassy-told-police-not-to-investigate_3167304.html