It depends, of course! In PPO's, normal office visits can be subject or non-subject to deductible. I have seen both. It sounds like, with the $20 co-pay, you are not subject to deductible. These plans are still out there but are not common. I would ask for clarification.
The 2nd question you need to ask is what is your out of pocket maximum? Co-insurance and out-of-pocket could have different definitions in your employers plan document. If it is $1500, that means that you are subject to $500 max expense per person, and once you hit $1500 total out of pocket everything is covered after that. That $500/per/person is going to be comprised of things like lab expense, specialist vists, and the 20% you are responsible for after deductible.
Because you do have that 20% responsibility, i'm a bit suspicious that your max out of pocket is $1500 for the entire family. Normally that 20% drags on to a much higher liability point.
I guess my bottom line is no one can be certain based upon what you've presented here. Don't be afraid to call and ask detailed questions. HR teams exist to answer questions just like this.
p.s. Sounds like a pretty good plan to me!