Libre Office has many settings that can affect its loading speed depending on the hardware you have. Graphics, Internet, network, sync settings, compatibility with other software, hanging updates, etc. You may want to check what it is you have enabled in writer that is slowing its load time. It has been my personal experience that it is a tick faster in Debian than in Ubuntu based distros, and it handles large documents a little quicker in Debian as well. This is probably because Debian is not cutting edge to the degree Ubuntu is, and there are less peripheral programs tied to it in Debian. I regularly work (nearly every day) with million word documents on my Debian box without any particularly annoying slow downs, but indeed there is a difference on my Linux Lite box when it comes to large copy and paste operations even though my LL box has twice as much RAM. I also use Libre office in Windows 10 with no problems either. It's a good bet some other program is slowing your Libre office load time, and there are many that can cause such a lag.
TC