Supported scenarios when installing multiple Office Products
We always recommend only having one version of Office on a machine and we recommend you use our most current versions. Having said that, there are times that due to adoption, testing, budget or migration strategies, it becomes necessary to have multiple versions of Office on a machine. There are certain combinations that are supported and others that are not.
Read more at source: http://blogs.technet.com/b/odsupport/archive/2015/12/01/supported-scenarios-of-multiple-office-products.aspx