What Heloc payment should I choose?

[Chris Connery]

So I am maxing out a HELOC on my primary residence to purchase my second investment property, an 8 unit.

Here's my question: Should I take the interest only payments at %5? Or roughly double my monthly payment by making it principal and interest amortized over 15 years? 

Here's my situation. I plan to sell my primary residence in about 5 years. I also plan to purchase more investment properties within the next 5 years. 

Thanks