Big databases are the main reason for which your Notion can be slow. Fortunately, there are things you can do to remedy.

1. Create filtered views of your databases and linked databases. Instead of displaying the full length of your database with all its items, create filtered views depending on your tags, dates, status, etc. This will help Notion as it won't have to load all the items or all the properties.
2. Limit the number of linked databases you have on your pages. Use them only when necessary / useful.
3. Still on linked databases, you can limit the number of items to be loaded. If you sort your database to see the most important / urgent items first, you won't miss anything (plus, you can still load extra pages at the bottom of your linked database). To limit the number of items, go to your linked database settings → Load limit.

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