This does not happen with upstream builds so this is a Solus problem. It's slow especially when typing hebrew text.
Libreoffice doesn't make intensive use of the GPU. I think it's used only to draw the interface and OpenCL may be used in Calc to speed up some calculations (Tools -> options -> OpenCL). You can go in tools -> options -> view and disable Hardware acceleration / anti-aliasing to see if it helps.
There are many tweaks to seep-up libre office, just search for them in your favorite search engine. One of them is to disable Java if you don't need it (most people don't): Tools -> options -> advanced).