[ubuntu] LibreOffice slow with large documents

Hi - I am ruing Ubuntu 16.04 (new install rather than upgrade from 14.04). I have used OpenOffice/LibreOffice since about 1998 with little in the way of problems. The upgrade from LO 4.xx to 5.1.2.2 with 16.04 is causing problems with large files (e.g. about 100 pages of Writer with diagrams etc). These documents have been going fine with the old version but for the first 3-4 minutes after loading they are unusable (periodically grays out and temporarily locks up). I have changed the settings in Tools->Options->Memory to have 300 MB "Use for LibreOffice", 3MB "Memory per object", remove from memory after 10 min, cache for inserted objects = 325. This has made no difference.

Also one of these large documents had about 20 blank pages added into the middle of it.

I am not really liking LO 5!!

Any ideas would be greatly appreciated.