SOLVED!!!!
so I solved the problem (for me at least)...

I used the command... -malloc=tbbmalloc in startoptions since your last info.

something must have changed since one of the last updates... after replacing it with the new setting "-malloc=tbb4malloc_bi" in the launcher everything is fine again... :)

now my settings are...
-no Benchmark
-noLogs
-noPause
-enableHT
-malloc=tbb4malloc_bi

the Problem was solved with one of the former updates (which one exactly I can`t tell, cause I had no time)...sry..... but!!

... with the DEV update yesterday 12.01.2016 I get the same issue... as mentioned before... appr. 13min. and then drop of framerate to 1-3

maybe there is a connection to the report of DnA:

ENGINE
Added: Aligned allocators are back on Dev Branch. Please report any significant new slowdowns / performance issues

ok the files are uploaded...

I´ve the same Problem... in singleplayer... with and without mod`s... after about 15-20min. framedrop to 0-3 Frames....same artefacts...

I tried other malloc, startparameter aso. nothig did really bring an solution...
(temp. check`s, memory check`s, perfomance logging... )

But.. once, it changed between updates... but the next update it started again... so I think, there is nothing to do from our side...?!

my opinon... would be cool if this annoying problem disappears... :)

Hm your right Cafeine, mods interfere, but it doesn`t happen in 2d editor... so I think its a 3d Editor problem?!