Hi Felix,
In order to provide recommendations further, I'd suggest submitting a ticket to Campaign Support. We'll need to review the data trying to be inserted along with the hardware resources being used and the overall health of the system in general.
If the environment is entirely on your side, we can still assist, but would recommend reviewing the following:
1) System resources on both sides are sufficient
2) Network is stable and bandwidth is available
3) How large is each row of data
4) Are you inserting data into active tables that other queries may be utilizing and thus locking the table
5) MySQL version and database being inserted into (if on premise), if hosed then it's assumed PostGres.
Also please let us know what kind of performance you are expecting.
Thanks,
Craig