1. That's JSIL not il2js (separate projects, similar goals)
2. That's using JSIL's custom JS xna reimplementation - not necessarily comparable. If you want to compare with real monogame, you want http://hildr.luminance.org/MonoGame/Platformer2D/ which is Actual MonoGame compiled to JS. (Not that it's fast - MonoGame does things that are fast in desktop GL but very bad ideas in WebGL)
3. JSIL output is currently slower than hand-written JS in most cases because VMs are really bad at optimizing .NET-style static types. A future version of the ASM.js spec will enable using it for managed languages like C#, at which point a compiler like JSIL will be much faster than hand-written JS.
P.S. Unity's IL2CPP compiler provides asm.js-level performance for a subset of C# right now; they use it for the HTML5 version of Unity. It's pretty awesome and well-engineered, so I'm hoping they open-source it. (I worked on it in the past, albeit briefly.)
2. That's using JSIL's custom JS xna reimplementation - not necessarily comparable. If you want to compare with real monogame, you want http://hildr.luminance.org/MonoGame/Platformer2D/ which is Actual MonoGame compiled to JS. (Not that it's fast - MonoGame does things that are fast in desktop GL but very bad ideas in WebGL)
3. JSIL output is currently slower than hand-written JS in most cases because VMs are really bad at optimizing .NET-style static types. A future version of the ASM.js spec will enable using it for managed languages like C#, at which point a compiler like JSIL will be much faster than hand-written JS.
P.S. Unity's IL2CPP compiler provides asm.js-level performance for a subset of C# right now; they use it for the HTML5 version of Unity. It's pretty awesome and well-engineered, so I'm hoping they open-source it. (I worked on it in the past, albeit briefly.)