I found this reddit thread which claims to speedup by increasing the threshold of the bytes consumed before garbage collector is invoked.

gc-cons-threshold is a variable defined in `C source code'. Its value is 800000 Documentation: Number of bytes of consing between garbage collections. Garbage collection can happen automatically once this many bytes have been allocated since the last garbage collection. All data types count. Garbage collection happens automatically only when ` eval ' is called. By binding this temporarily to a large number, you can effectively prevent garbage collection during a part of the program. See also ` gc-cons-percentage '.

I bumped up the value to 108, purged the memory and fired up Emacs and got 8.7 seconds. This was just few milliseconds less than original value (9.1 seconds). This is not very impressive, further I'm not sure how much of this improvement can be attributed to gc tweak and how much to cached memory (I'm not sure which all files are purged).