Version 6.3 add a new option for file search (
[INDEX FILES] ... highlight = fvh ...
This option will make search speed improved significantly (10x) when the search results contain large pdf/doc files. But you need to rebuild search index if you want to add this option.
You can do it during the weekend. If you have a Seafile cluster, you can add a new backend node to build a new search index and switch to this node when it is done.