Total number of parking spaces

Hello, I am working on a museum project with an existing building that is not a part of the scope. We are putting in 22 new spaces (2 new ADA, 2 new fuel-efficient spaces and 18 visitor parking spaces). However, there are 15 existing spaces that are currently serving the existing building. Do we need to account for them in our total number of parking spaces? We are pursuing Option 4 for SSc4.4 and our ITE is 34. If we do have to account for the 15 existing spaces, than we are 3 spaces over our ITE calculation. Any advice you might provide would be helpful. Thank you.