I am not sure what counts as a short lesson, but the seven second delays were on a lesson with 829 words (about 10% of which were “new” words). Trying the same lesson this morning, response time is faster - around one second for several words, then slowing down to a rather frustrating three seconds per word for a while, then back to around a second for a while, then back to three seconds, and so on. As mentioned above, a one-second delay per word is about the maximum my patience can handle, before abandoning a lesson and going off to do something else.
As a double-check, I just tried several absolute-beginner lessons in the following course Login - LingQ where lesson are less than 100 words each. Here performance per word ranged from almost instant to one second. It was certainly a noticeable contrast to the performance with the size of lessons I use in practice. If the performance were the same for non-trivial lessons (i.e. those that are several hundred words long) I would be quite content.