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I'm playing this game on 15" MacBook Pro Retina Late 2013 (it has quad-core Core i7 and Iris Pro).

Running it in Full Resolution (2880x1800) on High settings gives about 7 FPS... on Medium about 10 FPS and about 15 FPS on Low.

If I lower the resolution to 1280x800, on High settings I get about 30 FPS, about 40 FPS on Medium and about 55 FPS on Low.

From what I've seen from laptop benchmarks, people who play "Tomb Raider 2013" on Iris Pro graphics in 1366x768 resolution, get about 35 FPS on Hight settings, about 60 FPS on Medium and over 120 on Low settings.

And although graphics in "Sir, You Are Being Hunted" are nice, it's not more detailed than "Tomb Raider 2013"... it doesn't need to be more detailed than "Tomb Raider 2013"... SYABH is fun as it is, but I think that it could be more optimized than it is now.

Would it help if developers updated it to use Unity 5? I'm not sure which version of Unity it uses... but I read in some article about SYABH and Unity 4 was mentioned.

I read that Unity 5 brings performance improvements.
Late to the party, but this sounds like and issue with your machine to me. While SYABH definitely has optimisation issues, I can run it at 45-55 FPS on high settings in 1920x1080 on my machine (i5 quadcore and 2GB AMD GPU).