Microsoft introduced revamped forms in Dynamics CRM 2015 update 1. The new forms improve loading performance by up to 300%. The enhanced rendering engine keeps the loading time to a minimum, regardless of the number of fields displayed on the form:
Further details can be found at https://blogs.msdn.microsoft.com/crm/2015/04/29/microsoft-dynamics-crm-online-2015-update-1-new-form-rendering-engine/.