First of all LODs are everything. Hair groom are THE most expensive of all grooms, you should start with it.
Open up your groom’s file, go to LOD tab on the right and change the LOD 0 settings to your liking. Changing only “Curve Decimation” to 0.1 made a lot of performance boost for me, but other settings are interesting too. Don’t forget to delete\edit other LODs.
Additionally, you can reduce texture size for MH materials, here’s tut - https://www.youtube.com/watch?v=YvB_drutelc.
Moreover, try forcing LOD of your MH mesh component in “Level Of Detail”, you don’t need 64k triangles, LOD 4 with 3k triangles - seems nice.