Silver - The 1.5" is an average lower you should expect, might be a bit more, might be a bit less. As for using the OE struts, the reason it's best to replace them is because when you lower the car you are compressing them more then they are designed to be compressed when the car is just sitting there. You are basically losing out on the extra inch or so of travel they are designed to move and absorb bumps.
Will they still work? Yes, but they are much more prone to bottoming out and may go bad sooner because they are constantly being overworked. You will still see improved performance because of the lower ride height, and I would definitely get a sport shock when the time comes, but for now, this would get you by and give you the look you want.
Let me know if you need anything, and I hope this helps.
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