You could try disabling shadows in your graphicSettings.lsx, as there is no option ingame to do that and it gave a ~20 fps boost for me:
Code
<node id="ConfigEntry">
    <attribute id="MapKey" value="ShadowsEnabled" type="22" />
    <attribute id="Type" value="0" type="5" />
    <attribute id="Value" value="0" type="4" />
</node>