The length of the string exceeds the value set on the maxJsonLength property in SharePoint 2013 list form

I am getting an error when I open a SharePoint list display/New form.The list have couple of lookup columns. The size of lookup lists is big (around 20K items)

A Variable called WPQ2FormCtx load all lookup lists titles with ID in page view source.

The var WPQ2FormCtx exceed the maxJsonLength property. 

I tried to change the property in web.config, which does not resolve the issue. Is there anyway to stop loading var WPQ2FormCtx  in SharePoint list forms?

ULS Error:

System.InvalidOperationException: Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.   
 at System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, StringBuilder output, SerializationFormat serializationFormat)    
 at Microsoft.SharePoint.WebControls.ClientFormManager.OnPreRender(EventArgs e)    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Control.PreRenderRecursiveInternal()    
 at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)