Are either computed observables or are they both plain observables?
If one or both are computed observables then it might be worth putting a console.log at the start and finish of each one to see how often they're being evaluated due to changing dependencies. Maybe it's many times?
Another approach to debugging would be to make your if binding redundant for the moment by making it
<div data-bind="if: true && Logined() && Message().length > 0">
That ought to evaluate quickly due to short-circuit Boolean evaluation. Try it with false instead of true. Does the page still act sluggishly? If so then you've got something else that's slowing down your browser and it's just that the evaluation of this if binding is a casualty.
You could also add a
<span data-bind="text: ko.toJSON( Logined() )"> </span> tag to your page. Do the same for Message().length. Do they update quickly?