Discovered – currently not indexed - How to reduce this

Thanks in advance. Have read quite a few posts to do with 'Discovered – currently not indexed' and it seems like we're using all of our 'crawl budget'. We've got a bunch of new pages that are high quality in terms of content that we've submitted to Google through our sitemaps. And almost all of the pages are 'discovered - currently not indexed'. The pages are slowly going from that status to being indexed which is a positive, but it's incredibly slow.

I'm wondering if there's any strategies that I can do to speed this process up, here are some ideas:
1. We submitted a lot (hundreds of thousands) of pages at once to Google, so it might seem like spam (despite it not being), would it be worthwhile removing the total amount of pages in our sitemap now or is it too late?
2. Would it be worthwhile trying to remove any pages (or reducing their priority somehow) that are currently being indexed (old pages) that we don't think is necessarily as high in priority as these new pages to make room for these new pages?

Some example pages: (this is high quality content you can't find elsewhere)