. . . . Will Photo Story Dexluxe 2016 allow you to shorten a video clip? . . . .
Yes providing the video is in a supported format and you working in Timeline mode - see image below.
If you have not read it, there is a pdf manual installed with the program under Help.
If you have not yet purchased the software or are testing the trial version and are intending to do a lot of video editting I would recommend you look at Movie Edit Pro 2016 Plus or Premium - a trial version is available - Photostory is not as versatile as MEP.