While we try to support older versions of CAD engines, the space taken by product/version specific files starts to add up. Based purely on history, we assume Bricsys will release a 19.0 version this fall. At that point we will of course add 19b.dll files to our products, but at that time we will be dropping 15b/16b. The supported versions at that point will be 17.0, 18.0, and 19.0. If this is a serious problem, please contact our support email.