yes, it's a really clumsy sentence. "...has a low speed." How can we express it without a whole description? 'The bus is traveling at a low speed.' But this is not the level for so much context. Maybe we need to replace it.
it's not that the sentence is clumsy. I think it's a situation that a literal translation creates awkward results. In English I would say: "the bus travels at a low speed" and in Greek "το λεωφορείο πηγαίνει με μικρή/χαμηλή ταχύτητα"