This goes back to my original post regarding this issue. More components are going to generally be more expensive due to each landscape component counting as a draw call. This also means each component will be receiving a per object shadow which can get quite expensive very quickly if you begin to use dynamic shadows.
If you would like you can share with me your project, but I have a feeling that what you are reporting is an expected cost with the amount of components being used. Either way, you can zip up your project and upload it to a shareable drive link and share with me in your response. I highly recommend you watch the stream I did as well as read the documentation to get an understanding of how and why landscapes have certain sizes that work better than others.
Thank you,