300 ticks is the optimal size for most APIs, only a few need smaller sizes. This has something to with TCP/IP packets. Internet routers are most effective with packets below 5000 bytes, as normally generated by 300 ticks requests.

I do not know the IB data types, but you need the ask price and the volume for historical data, and that's what is requested.

And if you really get a "pacing violation" error, just contact support and describe how you did that. They'll look into it.