“Complete his training” is relative. If he’s already enough of a badass to freeze someone in mid-air with his mind at will,
It could be that little trick wasn’t even a Force power.
Maybe it was a piece of technology that created a "stasis shield " around an energie beam.Maybe is was a glitch in the edit, nope it was just as ridiculous as the rest of the film. I just got over prequelitis, now suffering severe sequelitis.
I seem to recall a great deal of Star Wars lore indicating that the dark side is the quick and easy path, wherein its weilders often learn powerful tricks swiftly, but at the cost of other skills, particularly with self mastery. I could easily see a Dark user like Kylo Ren, who is clearly powerful and talented, but also immature and lacking in self control, performing such a potent move, but in a rage motivated battle losing to someone inherently stronger.