I am level 15 but have only recruited 1 orange hero. How can I get more?

You have to earn recruitment tickets to recruit more heroes. Then use them in the Heroes Hall building. You will get a few for free every day, make sure you use these. You can get an orange hero from any ticket although the odds are higher with the orange Super recruitment tickets. It is still not a great chance though.

You can earn more tickets from events, daily challenges, Clash of zones etc. As well as completing the tasks each day to gain points. There are also other limited tome events that come along from time to time. You can also buy tickets with real money in various packages and the Arms Supply subscription.

You can also earn hero fragments from event rewards and Hero Tokens that can be exchanged for fragments. These are then combined into heroes, but it takes along time to collect enough.

But just keep playing and give it time. The odds of getting one are low but over time your will definitely get more.