So, there's a new release of Mathcad 15 M010 is available under "Order or Download Software Updates", here: https://www.ptc.com/appserver/cs/software_update/swupdate.jsp
File "Mathcad 15.0 M10 Read This First", which presented a list of bug fixes, on page "Reference Documents" for the present misses. But it can be found in the package installation program ("Help" -> "Read this First"):
List of bugs fixed in Mathcad 15 M010:
Other documentation on Mathcad 15 M010 (on the page "Reference Documents"):
"Mathcad 15.0 M010 Administrator's Guide" - https://www.ptc.com/view?im_dbkey=129421
"Mathcad 15.0 M010 Getting Started Guide" - https://www.ptc.com/view?im_dbkey=129423
"Mathcad 15.0 M010 User's Guide" - https://www.ptc.com/view?im_dbkey=129422