That is the fourth (4th) KB915597 Windows Defender Updates this month; i.e., April 1, April 5, April 8 and April 14.
You can see the list of threats addressed by this update and others at this Microsoft site … click <here>.
There seems to have been quite a few definition updates between 1.79.1432.0 and 1.79.1918.0 … so much so that 1.79.1432.0 has fallen off the end of the list!
Even 1.79.1918.0 has already been usurped by 1.79.1945.0. So we should get another KB915597 within days.
Good luck. I will try to keep you posted.
P.S., I successfully installed it … as well as the latest [i.e., April] Windows Malicious Software Removal Tool, KB890830.