I have been using LibreOffice for three years on my Mac (retina MacBook Pro 13", ssd and all) and it usually takes more than 20 seconds to start. It has been happening ever since the change to the new GUI. Is it just me?
I've since installed and reinstalled macOS X from scratch at least two times, and it always takes lots of time to start.
It takes about 2 seconds on my 8 year old desktop (2.5GHz Phenom II, SSD) running Debian unstable. 20 seconds seems excessively slow for your hardware. I wonder how long it would take to load in a Linux VM? That could eliminate the possibility of the hardware being a problem.
Thanks for your suggestion. So I've tested on a Xubuntu 16.04 installation on VirtualBox, and it takes 3-4 seconds to boot LibreOffice Writer. It has something to do with macOS X...
They updated the UI not too long ago (couple years, maybe?). I feel like format compatibility with proprietary software is more of a priority than being pretty, being a FOSS project and everything.
I've since installed and reinstalled macOS X from scratch at least two times, and it always takes lots of time to start.