There are two VOB files shown on your screen shot. Copy-drag (not move) both of them onto your desktop. Convert the VOB files to Mp4/AAC using the free download, Handbrake. You can get Handbrake here:
https://handbrake.fr/
After you have converted the VOB files drag the converted files into iMovie. Now see if you are getting the entire 16.5 minues. Also, make sure that you have sufficient free space on your drive to receive the movies. Movies imported into iMovie will be stored as full size copies, thus doubling the storage space used on your drive.
To rule out a corrupt preference, open iMovie while holding down the Option and Command keys and selecting to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects. {EDITED}
Another thing to try is to create a new project and import your movie into the new project to see if it plays all the way through. Sometimes issues are confined to only one project and will not appear in another project.
-- Rich
-- Rich