Slurping a 15MB file into an array (longest line 357K) only took 3 wallclock seconds on my lowly PII300, so I think you really need to show us what you're doing, like BeernuT and crazyinsomniac ask.

One thing I will say though, is: the fastest way to read a file isn't the most obvious:

Using that method, I can read the whole file into a scalar in 0 wallclock seconds! :)

    --k.