In order for Distant Horizons to enable huge render distances, it needs to generate LOD models for the terrain. But this is limited by the servers max render distance it sends to the clients, which is at maximum 32 chunks. Normally this would require manual exploration of every client.
I prepared a pregenerated cache of LOD models for a huge area around spawn.
Installation
Open the root of your minecraft Instance in a file explorer. This is where folders like these:
Download the distant-horizons-cache.7z and extract the contents into the folder you opened in step 1. After you should see the Distant_Horizons_server_data folder in your minecraft Instance root folder.
Make sure the folder name inside Distant_Horizons_server_data looks similar to the entry in the ingame Server list (ignoring obvious formatting weirdness)