Rails collection select when collection is way big

I have a form partial inside which I select associated users through a multiple: true collection select:

    = f.collection_select(:user_ids, User.all, :id, :email, {selected: @limit_group.user_ids, include_blank: true}, {multiple: true, "data-placeholder" => "Add users to group"})

But how can I do this more efficiently to avoid big load times when the database has like thousands of users?