This is dependent on the version of the Simulink. In newer versions, the company has claimed that MATLAB run speed has been increased, but in practice this has not been proven for me (I use core I7, RAM 8)!!! Of course, newer features in newer versions added that has many benefits, but being heavy is still the main problem of this program. I recommend that if you dont need a specific block diagram in Simulink, use older versions of MATLAB like as 2010 or 2011.