I did another whole round of OS re-installs to verify, and was able to confirm, that on both Windows 7 (Catalyst 14.??) and Windows 10 (Catalyst 15.7.1), inside of the debugger, grGetFormatInfo GR_INFO_FORMAT_PROPERTIES has a huge time delay. Enumerating all of the formats takes like 10 minutes, whereas outside of the debugger the enumeration takes about a second, more or less. When I add a test for the presence of the debugger and bypass the call to grGetFormatInfo, the remainder of the code runs as expected.
Thanks for posting. I've passed on the question to the Mantle team -- the experts there should be able to answer your question.