Honestly, start with educating yourself. It doesn't even need to take a lot of money. Read posts, blogs, books etc. Join a local REIA in your area, attend meetings, network, talk to others about what they are doing, how they got started etc. You need to study your local market and understand where profits can me made, because the same strategy may not work in the next city.
With $15k, you would need a partner or hard money lender in order to fix/flip, plus you need to find the great deal, find reliable contractors (which is the hardest part of fix/flip)
Bird-dogging or wholesaling can be done with the money you have but dont let the guru's lead you to believe it's easy and no-money needed. The wholesalers I know work hard, they talk to A LOT of people. They have a 100:1 ratio of people to possible deals. They spend money on marketing, mailings, driving all over the place.
I'm relatively new to RE investing. I took a year before I made any moves to understand it, to learn what I wanted to do. I found I needed to have the end in mind, why real estate? What can real estate do for you that other investing cant? Do you want to be active (a job)? Or truly invest (passive)?
What ever you decide to do, take your time, educate yourself, be patient. Dont rush in because you think prices are going up and you will miss out. Money can be and IS made in every market, regardless of what the news tells you.
Good luck.