You could do it this way, but you'd have to ensure that what you're investing in has a return that is higher than the value of the loan that you're taking out to pay for the other 15k in the mean time. That would also have to include the deductions for putting your money in and out of the investment as well as any tax (as mentioned above). i.e. to cover the 9% loan you'd need a minimum return of say ~18%OK but what i mean if I have £30k in the bank and I wanted a £30k car I would put £15k on the car and the other £15k on something that will appreciate like a business or something like that...
Pedro
If you can find regular investments with that sort of return then I'd say that there's no point in even contemplating doing things in this way as you'd be rolling in cash before too long so you should wait and pay with cash and still have plenty to invest elsewhere. Unfortunately I don't think they exist regularly or predictably enough to be able to base a long term income on.