I second what others have said... don't take out a loan for the value of the car + mods. Because if the car is ever stolen or totalled, the insurance company is going to give you the value of a regular teg (if you even have full coverage) and then you'll be stuck paying the rest to the bank for a car you wouldn't even have.... be a pretty crappy situation. Granted, some insurance companies are cool when it comes to mods but don't plan for it... and that's once again, only if you are paying for full coverage.
Also, if you are looking for a '00-01 clean, low mileage GSR... don't expect to have too much of that $15k left to make a dent into really doing much with mods, especially after you buy a quality JDM conversion and get it painted, etc. Of course, if you take my advice from the first paragraph you would maybe just take out a loan for whatever car you want + a JDM front end. But from there, I would work to pay for future mods... don't spend money you don't have, you'll only get yourself in trouble