How many links are too many for EPUB?

I have an ebook with a large number of internal links. The stats are below. I’m trying to understand if my troubles are related to the Kindle Previewer or to some unspecified limit on how many internal links an EPUB can practically handle.

The finished EPUB size is about 3.6MB. The contents are mostly word lists. The two largest lists have 77k words each. Some shorter lists and prose instructions round it out to about 160k words. The lists are divided into about 1,500 HTML files. The lists have extensive cross-linking, about 406k links. I used EPUBcheck 4.1.1 to validate the EPUB (version 3.0.1). I have many warnings about the .html suffix on my files, but no errors.

The Kindle Previewer needs roughly 25 minutes to load the book. Once loaded, it does work. I can navigate correctly between word lists. Most words link to another place in the lists. These cross-links work. However, after a few minutes, or maybe some number of link clicks, the Previewer freezes up.

Are there other ways I can test this EPUB? I’d appreciate any help.