If you want to keep the pixel size of the photo the same the low quality export option will only get you down to about 300 KB. But if you reduce the pixel dimensions and the quality level at the same time you can reach the 100kb size.
For example I took a 3072 × 2304 pixel photo, 2.3MBs, and exported at 1800 x 1350 pixels at Quality level = low and got 127 KB. You'll have to experiment with size and quality level to get what suit your needs.