If I'm not mistaken they'll receive low-res versions of the pictures then download the full-sized ones later
From the Planetary Society website
"On September 14, New Horizons will begin downlinking a "browse" version of the entire Pluto data set, in which all images will be lossily compressed. It will take about 10 weeks to get that data set to the ground. There will be compression artifacts, but we'll see the entire data set. Then, around November 16, New Horizons will begin to downlink the entire science data set losslessly compressed. It will take a year to complete that process."
From the Planetary Society website
"On September 14, New Horizons will begin downlinking a "browse" version of the entire Pluto data set, in which all images will be lossily compressed. It will take about 10 weeks to get that data set to the ground. There will be compression artifacts, but we'll see the entire data set. Then, around November 16, New Horizons will begin to downlink the entire science data set losslessly compressed. It will take a year to complete that process."