You should set ga() to pass all of the generation members at once using UseVectorized option. Then you set the objective function to be calculated for all of the members in parallel using parsim() and SimulationInput object. The general framework is to create an array of SimulationInput object, which has one such object in each element. Each element contains the variables set from the corresponding rows of the generation passed by ga(). The objective function receives a PopulationSize-by-nvars array and returns a PopulationSize-by-1 array. https://www.mathworks.com/help/simulink/slref/parsim.html
You can also benefit from options of parsim to run even faster, including fast restart, rapid accelerator, etc.
