Mayby to late; or a cost issue, but omit 615, and go for 635/655, and you can stay on 8.10; 4-5 more years.
With 615 you need more radio planning, hence the fact of only two radios, and some frequency issues.
Spectrum Analysis Support for AP-615
- The Spectrum Analysis feature is not supported on AP-615 access points.
UNII-4 Channel Support for AP-615
- AP-615 access points do not support UNII-4 channel.