@Joel Fine excellent question! I've spoken with a lot of different turnkey companies and it annoys me so much that they never include placement or renewal fees in their pro-formas (not that you should trust their pro-formas anyway). I think on average over time it will probably be closer to 15% like you have calculated, but in reality, its going to be lumpy.... a $1,000 placement fee could wipe out half of your return for the year!
For my projections (to be conservative) I'll assume an 18 month lease with two different PM lines. The first line I have the standard 8% PM fee, and on the second line, I'll do a placement fee in year 1, a renewal fee in year 2, and then a placement fee in year 3, etc. That may very well equal 15% on an annual basis, but for me it helps to think about them separately as the 8% should be constant, but the second line will be variable.
For my homes in Memphis, I'm paying 8% PM fee, 75% of one month rent for tenant placement, and $150 renewal fee. I also have an optional 2x/ year property inspection for $80 (I've chosen to get it done once a year). This is not the cheapest I found in Memphis, nor is it the most expensive. It's in the middle.
Finally, I had a rough start to my first two turnkey purchases. I've learned the hard way to value of a good PM and I have no desire to independently manage them remotely. A great PM is worth their commission, but a bad one will drive you crazy (and cause you to lose money).