Depends on the mode the satellite is operating in. Typically: a full disk image every 15 minutes, the continental USA every 5 minutes, and two selected "mesoscale" regions (they will move around based on interesting events) every minute or even 30 seconds. Not all these products are relayed through this downlink though. On HRIT you'll find a full disk image across 7 different spectral bands every 30 minutes, and mesoscale images across 3 different spectral bands every 15 minutes.

Next to this data, it also contains relayed images from GOES-15 (GOES-West), Himawari-8, EMWIN data, and NWS forecasts and plots.