How to make a copy a custom Entity

I have a CRM 2015 On-Premise system.  The server which houses the DB has a Windows Server 2012 Op Sys and uses SQL Server 2012.

I have an entity called 'Application.'  Originally it contained about 100 attributes/fields.

My company hired a vendor to come in and create some enhancements to our existing system.  In doing so, approximately 200+ attributes were added to the 'Application' entity.  The addition of all of these fields caused our system performance to plummet!  I have written several SQL queries that are based on our 'Application' data.  Most of these SQL queries are very simple - 10 fields or less are pulled from the 'Application' entity in order to create a report.  Some of these queries are run quite frequently by our users.  It has been found that these queries are running very slowly - sometimes it takes over a minute to retrieve 6 fields from the ‘Application’ entity!  However, what needs to be remembered is that each record in that entity now contains 300+ attributes.

What I am thinking as a possible solution to our performance problem  is to "split" the existing 'Application' entity into several other entities, each identical to the other except for the name, GUID, and whatever else needs to be different in order to uniquely identify each entity.  I would then eliminate from each entity all attributes except those that pertain to a specific "area," thereby reducing the number of attributes on each “new” entity.

Before the addition of the 200+ attributes, our CRM system ran rather efficiently.  Now, not so much.  And, the poor system performance is negatively affecting our company's work performance.  We are a service organization, processing hundreds of clients each day, and we need to be able to process applications as quickly and correctly as possible.

Any suggestions/advice would be GREATLY appreciated!