You have reached the maximum number of 15 object references
You are attempting to edit / add cross-object formula fields in your Org and encounter the following error: You have reached the maximum number of 15 object references on 'Object Name'
This error is due to a Salesforce limitation of 15 cross-object formula fields per object.
Please review the following Salesforce Knowledge Articles for additional detail:
Upon request, Salesforce Support may be able to increase this limit from 15 to 20 for you, however 20 is the hard maximum limit.