It’s showing as increasing the loan amount although monthly interest payment stays the same? 

The increase in property taxes, insurance, and maintenance/wear and tear may erase all of your gains and more. 

Unique features like land and outdoor amenities can add value, and utilities can increase rent.

Second, your tax prep fees would increase dramatically.

Other factors of condition, schools, and rental increases are some of the other factors to consider that will not appear on a spreadsheet.

This doesn't mean you should be looking at markets such as Detroit and Memphis, because even though it looks good on paper, if they are shady neighborhoods, you are going to spend a considerable amount more on property preservation (broken windows, stolen HVACs, etc.).The easiest way to increase cash flow would be on your existing property.

Refi'ing into a 15yr loan is likely to both increase your effective rate and crimp your future buying power by increasing your DTI. 

I would tithe on my increase, which would be profit whether you take it home or leave it in the business.

I had a less expensive one and it did increase, but not a lot. 

The market was increasing and we were able to find an off-market deal from some friends who held the property for over a year had no interest in fixing it up.