Hi vlad59,
Your answer confirms my suspicion that it is not COPS but the Pi itself that may be the "problem".
I'm running my Pi for 99% from a Hard Disk (system and data), so no latency from a flash drive. But I noticed that the USB port on a Raspberry Pi is rather slow. This in turn reflects on the HDD and network performance.
I will try to install apc on the Pi and see if it can speed things up a bit.
Will report back when I have some results.