There have been threads about this for the past few days / weeks on Reddit and other places where people discuss SDRs and satellites. The topic also came up in 2018, when the satellite appeared to be having similar issues. NOAA released an official statement yesterday.

I’ve received some good images from NOAA 15 in my short time decoding APT, so it’s odd how rapid this deterioration / recurrence of problems is. Here is a recording from a pass just minutes ago:

7-23-2019: NOAA 15 satellite image, processed with Contrast A preset

Processed with Normal preset

Processed with HVCT preset

Processed with MSA preset

This may be EOL for NOAA 15.

(7-25 @ 8:55PM CDT) Update: While NOAA has yet to release further info, people are claiming that the satellite is transmitting normally again.