Try disabling wifi power saving:
Run the following command to auto-generate an iwlwifi driver options configuration file in /etc/modprobe.d/iwlwifi.conf:
echo -e "options iwlwifi power_save=0\noptions iwlmvm power_scheme=1" | sudo tee -a /etc/modprobe.d/iwlwifi.conf
Or, run this if the above command is no better:
echo 'options iwlwifi power_save=0 d0i3_disable=0 uapsd_disable=0' | sudo tee /etc/modprobe.d/iwlwifi.conf
Reboot after the creation of the configuration file.
If the new iwlwifi driver options file produces no improvement after rebooting it may be deleted.
Also, I believe this adapter has speed issues when TSO is enabled, as there is some bug with the driver.