It's marginally better because it explains what you mean, and that at least eliminates other nasty interpretations.

However, I don't think it's fair for you to assume they're "trying to hide that it's so slow". There's no need to impute bad motives to people, and you don't have nearly enough information to justify such a claim.

What's wrong with simply reporting the problem that you're experiencing with the software? That would make your comment helpful, with no trace of a putdown.