Using cygwin with ImageMagick installed you can resize entire directories of jpegs using the convert utility

for i in `ls *.jpg`; do convert -resize 30% -quality 80 $i conv_$i; done

The 30% made images with a resolution of 3072 x 2304 pixels (approx 1.6 to 2.1MB each) into 922 x 691 (approx 80KB to 140KB each)

Experiment with different percentages to get your desired size.