Thanks, Stefan, but I already tried that - the thing is:
If I split the document in halfs (p 1-50 and p 51-102) both halfs show the same problem although they both are slightly faster. If I split both halfs into 4 parts the speed improves again for
all 4 documents. If I split those again, all remaining 8 documents (they have only about 10 to 15 pages and <70 KB each by now) save with a normal speed.
That clearly suggests that there is no "damaged part" at all in this document but Word 2013 can't handle it the way it should as soon as it get's large... Also the speed get's worse with the increasing
length of the file not with the increaseing size (it doesn't get worse if I add a picture however it does if I add more pages).
If I didn't know better I'd say the problem lies within the style sheets. But as already said: Even if I delete all custom style sheets, there is no improvement...
Is there anything else that Word might have trouble with?