If I live a busy life and don't have the time or care to invest on my own, but want to put, lets say $200k to work, is a 15% cash flow return reasonable? 

That's smart business, right?

The other way I fund deals with none of my own money is using a private lender that I have years of experience and relationship with and/or using HELOC and other business lines of credit.

Years in business?

From real estate investors to other small businesses, I talk to people daily who have no idea about the potential liability under the Telephone Consumer Protection Act ("TCPA")(47 U.S.C. 227 et seq.).There are two initial issues that can create huge problems with your suggestion.

My business partner and I purchased a commercial office building a few years ago with creative financing.

I also believe that I should also invest is my business.

There may be a way to reduce property tax reassessment by using LLCs, but it is a complicated plan, takes time to complete, generally needs a business purpose, and is not without risk. 

"owned outright"- do the members have personal debt to support this, or is it both zero for personal and for the business?

My business partner has two STRs adjacent to ours that has several 1-bed units that rent very well during the week.