Sell the 1.5 BTC when the price is high enough. For example: say you sell it at an exchange like Gatecoin.com for $500, which means you have $750 in cash. Then buy bitcoins when the price drops down to $400, which means you have 1.875 BTC.
The second time around, you will sell 1.875 for $500 again. This time, you will get $ $937.50 in cash. Then buy more when the price is back down to $400, which will get you 2.34 BTC.
Repeat this process!

Or sometimes you may notice that the price for Bitcoin for sale in an exchange is more expensive in USD than in EUR. You can make quick and easy money by buying the bitcoins in EUR and selling the bitcoins into USD.

Whatever you do, make sure you are dealing with a legitimate exchange by doing your research. Exchanges that are not transparent to their customers is a big red flag.