If I say ok Google set alarm , Google brings up set. Or if you ask it about the national football league it will look up national. This is on my moto x.
I have the same problem on a Moto X v2 (XT1095), Android 5.1.
If I say something like "navigate to blah blah" it only gets "navigate" and beeps, same for most of the commands, only gets first word, no matter how fast I try to talk. Makes it just about useless. Used to work a version or two ago.