Learn English – The meaning of “have long said”

It's not common to use "after a long interval" to mean "after a long time." Your sentence "I had sushi for the first time in a long time" sounds perfectly natural.

For me the text "in the last two weeks" means not more than two weeks. I might write "in just over two weeks" to indicate a small number of days more than two weeks but less than three weeks. For the purpose in the question I might write "I have uploaded 5 videos in just over two weeks". All the other forms I can think of take more words to qualify the "two weeks" to indicate a few days more than two weeks.

Using the text "in the last three weeks" means not more than three weeks and so matches the ideas wanted by the question.