Welcome Arnaud,
thanks for your interest in Vienna MIR.
Depending on the number of Vienna instruments enabled on your system and eLicenser, three minutes sound reasonable for me. Keep in mind that MIR is a full-blown VSTi-host, so it has to take care for your VIs, too. ;-)
Re: Venues - Please make sure that you download and install the Demo RoomPack, too. This will include one microphone position (but of course all IRs from the stage) recorded in the Mozart Saal of the Vienna Konzerthaus. - The actual RoomPack 1 that comes with the retail-version offers a total of five venues, recorded from four main microphone distances each, which actually gives you 20 individual venues.
The "Default" is just one stage position of the Grand Hall of the Vienna Konzerthaus, and these are the only IRs that come with the MIR-engine itself (just to make sure that one can check the functionality of the system without having to load a complete Venue, which again may take up to a minute, depending on the number and length of the included IRs).
Kind regards,