As far as I know, it is not possible to predict the final file size, as file format and compression do depend a lot on the content of the images.
A first step in the direction would be the Image Processor script.
Hope this can help.
1500x2000 is a 3:4 portrait aspect ratio. Image that do not have a 2:4 aspect ratio would need to be cropped to a 3:4 portrait aspect ratio. Before fitting to 1500x2000px. Landscape and wide panoramas will not crop well to a portrait aspect ration the composition will be very different.
File size depends on how well the image compresses. Jpeg file uses a lossy image compressor. That has a quality setting a high quality setting produce larger files then lower quality settings. I find I can not see with my poor eyes any difference in image quality between a quality 10 file and a quality 12 file. So I never save a quality 12 quality 10 file are quite a bit smaller than a quality 12 file.
Image with a lot of fine detail do not compress as well as images the have large areas of smooth colors. I created two identical 1500x2000ps image which were nothing more than a spectrum gradient. To the first one I added a large amount of noise so it would contains a tremendous amount of detail. I the save out jpeg files for the two images using quality 10, 8, 5, 3. and 0. So you would get the idea, At quality 0 the noisy image jpeg file was over 2MB in size where the smooth gradient jpeg quality 10 was only 232KB the young girl quality 10 was 765KB.