I think you'd be fine - the XF does a proper mirror lock up I believe. As in stay up until you tell it to drop (as in the Hasselblad H series). If memory serves, to activate, on the top touch screen tap the mirror icon, then shoot away with a LS lens.
You may want to set one button to the hyperfocal for the lens - what apeture & shutter speed are you looking to use? The thinner the DoF, the more it'll tattle.
If you want really quiet, one thing you may want to consider is doing an A body with the lens of choice - less parts, live view and if you're shooting low, using the iOS app.
-Joe