I have found that for some reason it is possible that the Description attribute of an entity is not included in the customizations file when exporting from Dynamics CRM 2015. If this is the case, then the system will crash during import when it tries to determined if the LabelDescriptionHasChanged.
You can confirm that this is the issue by running the following SQL script:
SELECT objectcolumnname, s.FriendlyName 'Solution FriendlyName', label, objectid, LanguageId
FROM [LocalizedLabelAsIfPublishedView] l
LEFT OUTER JOIN solution s ON l.solutionid = s.solutionid
LEFT OUTER JOIN entity e ON l.ObjectId = e.EntityId
WHERE e.name = 'new_entity'
Of course you'll need to change the new_entity to the schemaname of your entity. If this query results only the LocalizedName and LocalizedCollectionName but no "Description", then this is could very well be the cause of the error messages. Another way to confirm is to check the customizations file, search for the entity and determine if the