We plan to hold our primary residence and rent it out.

Jose,There are a few ways to answer this question, first if you can buy a Primary home then Yes, $15K is enough. 

@Zachary Dylan Nelson Do you currently own your primary residence?

The reason I ask is, I'm going to install updated fans in my primary residence which one day, will be a rental property.

To qualify for these owner-occupant, low downpayment loans, you have to live in the home as your primary residence for at least 12 months.

Me & my sister co-own a duplex and I would like to sell it and put the money toward my primary residence(sole ownership).

It is far more likely that a first-time homebuyer is going to buy as their primary residence.

You'd need to go with a cash-out refi since they purchased in cash and have no existing liens.If this is going to be your primary residency then I'd recommend the HELOC advice from above.

I currently own my primary residence and recently decided to buy a piece of raw land where my father’s construction company is, and with his help,  build a single family home on it which will become a long term rental when completed. 

My wife and I have the same strategy of buying a primary residence every year and then renting it out when we move to the next home.