When I add thirty or forty essential graphics in sequence, very lag

I have now added 40 essential graphics to a video to show the moderator's points or supplementary information, just one or two lines each.
But when there are moreessential graphics in the sequence, when I want to change the word or move it, it will be very lag. I have to wait for 2 to 4 seconds to select a word.
Does anyone have the same problem? How to solve?