Expanding network on a DL180 Gen6

Hi Guys,

The current HP DL180 server which I have is equipped with only 2 LAN ports. I'm having hard time figuring out whether the read/write operations slow due to the server (using only a single LAN) or because of the switches. 

However, I could see a massive amount of read/write happening as per ESXi logs and I would like to expand the LAN to allocate more bandwidth to the server using link aggregation. But I'm quite confused as to what would be the compatible to use the available PCIe slot.. if we can use?

Any advise will be appreciated.