Scene with high number of materials, hangs on auto-save and manual save

Normally don't have any issues with saving, but i'm working with a scene with a higher number of materials 50+ and every time auto-save fires or i manually save, my app will hang for ~20mins - have very fast SDD and no other programs open. Opening a smaller scene and is fine, file size is around 4Gb which isn't horrendously big...