In 2012 (and R2) you may get slow read speeds with the NIC’s teamed, but write speeds are fine (use lanspeedtest lite to test speeds)
To fix this go to each NIC properties, click the configure button, click advanced and set these options to DISABLED:
largesend offload V2(ipv4)
largesend offload V2(ipv6)
TCP/UDP Checksum offload (ipv4)
TCP/UDP checksum offload (ipv6)
This should take effect instantly.
Reference Highpointe Dental (highpointe-dc01) if needed