Certainly you can make 15% on your active investments, but when you factor in downtime of your capital between deal and other constraints, I think 15% across an entire portfolio is tough.Certainly it can be done, but if it's integral to your plan, you need a different plan. 

I own a landscaping business in Illinois and in the winter down time I try and purchase a rental or two.

It drives calls to my phone and traffic to my site and I usually have a great time selling something he couldn't move.Also do some rentals in your down time.

Also to work harder on the pipeline so there is no downtime and continue to chug forward without missing a beat.

Taking over a vacant 4 unit that requires turnover expense in each one plus down time filling them back up versus buying that same building with even halfway decent tenants in each unit can skew your upfront capital needs by a huge amount. 

It is still appropriate to include some expense for utilities as you are factoring in 8% vacancy, so you would have utilities expense during turnover, downtime, etc. 

There doesn't appear to be much downtime but I've only been up and running for a couple months so don't take my word for it just yet.

For example, a heloc, a private lender, 401k loan (specifically during down times, but that is a different topic) etc. 

You have to calculate lost rent for downtime of 1 to 2 months and make ready cost.So if unit takes 5,000 to completely reno with down rent costs would take about 2 years with a good tenant paying on time with no capex issues to break even.

Done property there should be very little down time on the unit and increased profits going forward.