Yes, it takes several SECONDS to open documents on my 15+ year old Windows 7 machine.
As for "advanced features" I do not know what you are referring to.
I have been using LibreOffice for over 10 (admittedly low frequency and not complex documents) but I have NEVER had it crash. I also know the head of IT for a medium size (250+ employees) that installs it on all of their computers.
It takes about 2.5 MINUTES to open a spreadsheet with more than a few tabs on a fast Window 11 box. My suspicion is that it doesn't handle larger files well, there is a lot of discussion about the issue on the Libre dev forums but no solutions unfortunately, it is a known issue.
The random crashes are also a known issue, lots of discussion and work but no complete solutions yet, unfortunately.
Advanced features like macros, pivot tables, etc. Saving to different formats doesn't work well either. For example, office can save a libre office file and it works fine in libre office, but an office file saved from Libre office will need some work to function correctly in office. The inability to go back to office after using libre is a big deterrent to trying it.
Kind of scary a business would trust it, it's definitely not stable or supportable in a business environment. Maybe they bought the commercial version that is supposed to be more stable.