Prebuild speed depends on your server resources, complexity of your site (themes/plugins), enabled features (Merge styles, Merge scripts, etc).
In order to speed up prebuild you can do the following:
- Enable Compute API
- Enable Prebuild Booster
- Set Prebuild to Unlimited or Moderate
Please note, that the first few pages can be slower, also the first time of prebuilding cache can be slower.