Simulation

Another possibility (maybe more readable, gives the option of a list, probably not faster):

Replicate(1000, rexp(15,1) )

  

provided that simplify=FALSE:

    is(replicate(10, rexp(15, 1)))
    # "matrix" ...

    is(replicate(10, rexp(15, 1), simplify=FALSE))
    # "list" ...

vQ