With your budget, please dont invest into BTC mining. I believe even a group buy would be hardly worth it.
15k wont get you even 5 ghs from any of the manufacturers (cointerra, kncminer, extremetech, bitfury etc).
A rig is a computer set up to mine. At this stage you would need a decent GPU - the lowest, R9 270x costs about 15-17k. Considering that the GPU alone eats up your entire budget, you have three options.
- Increase your budget to atleast 30k. Though 40k would get you better results
- Use the 15k to buy and trade coins
- Invest into a FD and earn 9%
If you do decide to invest more towards a rig, come back and drop a line. Im sure someone will help you out with configuration.