It is certainly a lot.
It is possible that some redundant data might be indexed. Usually the best way to reduce the size is to get rid off the potentially unrelevant information for the search.
I suggest maybe trying a few tricks to drastically reduce the size:
– Make sure only the required fields are selected. A very common mistake is when long text posts contents are being indexed, when the actual content is mostly less important for search as other fields. If you are using post categories, tags, custom fields or other taxonomy terms, then maybe turning off the index for post contents will do the trick alone. Usually the title, tags/taxonomy terms and the custom fields contain the more important information. That will drastically reduce the size.
– Using stop words filter for common words: https://i.imgur.com/ZZT1yuT.png
This one is definitely efficient as well, but you need to be careful with the words lis, so that important keywords are not removed.
After any changes you will have to recreate the whole index though, so I recommend making more changes at once. Also, for faster indexing you can increase the Post limit per iteration option, try with 100 posts, the plugin will automatically adjust during runtime: https://i.imgur.com/sAsQEGj.png
