Average photo size with iPhone SE
In a highly unscientific test, I just took 24 varied photos (textures, objects, macro, landscape, etc.) with my iPhone SE, with Live Photos off, and found the average size to be about 2 MB.

NOTE: my iPhone SE is running iOS 10, so is not using HEIC (High-Efficiency Image Codec) encoding, which can save approximately 50% of the file size without sacrificing quality. If you install iOS 11, you may find the images are significantly smaller.