Do I get taxed on capital gains if I didn’t sell anything?

Where are you seeing that you are taxed at a capital gains tax rate of 15% if you did not sell any type of investment or property?

You might have capital gains on a 1099-DIV for dividends from a mutual fund.  

If you own mutual funds in a taxable account, you will include as income your dividends, interest, and capital gains generated within the fund in the year they are credited to your account, even if you re-invest them.  

These will increase your overall basis and reduce any capital gains (or increase a loss) when you eventually sell the fund itself. 

You could see this tax from either qualified dividends or "capital gains distributions" that are reported on the 1099-DIV you receive from your mutual fund. 

If this doesn't sound like it fits your situation, let us know and we can work to help you find understanding of where this number may be coming from.