I'm sure LibreOffice has made some great advancements over the years on OSX. NeoOffice attempts to be LibreOffice that's closer to OSX's native look, feel, integration. https://www.neooffice.org/neojava/en/index.php
I have a Macbook Pro 2012 on Mojave with 4gb's of ram and it runs the latest LibreOffice like hot butter. You might want to try upgrading to Mojave if you haven't already. If that doesn't work, I would do a clean re-install of macOS.
Before all that, try https://www.neooffice.org/neojava/en/index.php or try an older version of LibreOffice. Also try resetting your Mac's SMC.