Yeah. They exist. Here is the only video clip of one. It is dramatically slowed down. It shows the reaction of the Fast Loris just before attacking its prey. (The cameraman did not survive)
The claim that there is a terrifying Fast Loris implies the existence of a terrifyingly Slow Loris. I dread the latter vastly more than the former, your concerns be damned.
Fun fact: slow loris was also the name for a really cool type of denial of service attack that would eat up the entire connection pool for a linux web server.