In the R Packages book, the CRAN notes in Chapter 11 has the following note about vignettes:
You’ll need to watch the file size. If you include a lot of graphics, it’s easy to create a very large file. There are no hard and fast rules, but if you have a very large vignette be prepared to either justify the file size, or to make it smaller.
It mentions there are no hard and fast rules, but what constitutes a "very large vignette" in CRAN's eyes? I have a vignette that is about 45kb --- per section 3.8 in R Markdown: the Definitive Guide, knitr::html_vignette
shrinks html vignettes to about 10kb.