3 MB is pretty big to start with. If you can retake the picture, your camera likely has other settings you can do to reduce the file size before you take it. For example, my camera has three different settings for JPEGs.
MY understanding is the RAW format doesn't compress anything.
Quote:raw image files are considerably larger than files saved in other file formats - up to 5 or 6 six times greater than the equivalent JPEG.
The image processing program I use also allows me to "export an image" at a lower quality, which will reduce the file size even more.