I would get your buttons to send the page number and page size to the server function, so the server function only returns the slice you need.
If you have sql access you can use offset and limit to get the exact slice you need, otherwise you can slice the iterator on the server side, much faster than slicing it on the client side. If you have a column with incremental unique values, you can use that with q.greater_than to skip to the page you need.