Wow ... first time using vMix 15 live, loving it.
Installed in a separate folder, opened (and modified) a template that I had made in v14.

Really happy with the functionality.
Discovered a bit late, that the window for IRP can be unpinned and then becomes larger with more controls.

Had a little trouble to Export the compiled fragments, got the error "could not find video for events".
In the end, chose the radiobutton Events - All, unchecked 'Export each event separately' and got a nice file with my (58) events.
Converted it from mpg to .mp4 with Mpeg StreamClip on Mac.

Got a blue screen on Win 8.1 Pro upon quitting Vmix, PFN_List_corrupt (seems more a Windows thing, than Vmix's)

Wishlist:
possibility to overrule the default 5 & 10 sec. durations;
for me, around 7 sec. (or 6 with playback at 75%) would work best when launching replays during a live basketball (Europe) game.

2 tips:
I stream via YouTube, and these settings really seem to help:
https://support.google.c...?topic=2853713&hl=en
The "Keyframe frequency: do not exceed 4 seconds" translates for me to a keyframe from vMix every 1 second
Using 720p
Chose "Main" instead of "Baseline"; High-option is not there for me.

Yesterday's game at

using vMix 15

Hardware:
i did IRP with one camera, and it works fine (system req's met) on this laptop:
HP Zbook 15 workstation (Quad Core i7 + 256GB SSD + 1920x1080) 16 GB ram
Win 8.1 Pro 64-bit, vMix 15 64 bit
cpu 4800MQ, 2.70 GHz
Onboard Intel 4600 (using that one by default), plus Nvidia Quadro K1100M, using the latter (exclusively) for vMix with profile: 3D App, Default Global Settings
Using the laptop's Thunderbolt port with a Blackmagic Design Intensity Extreme, working just fine under Windows (and Mac).

Same system also used with vMix 14 without problems; not liking the saving / auto-looping of Video Delay there, especially with vMix 15 beta now available.

Hats off to Martin & his crew !