I'm very experienced with this. I have several networks mixing both 1510 and 1522 series. (200+ radios in one). It used to be true that the 1522 had to be the RAP, but this is no longer the case. You can mix and match all you want. Just remember the basic differences in mesh data rate between them. And of course, neither series will talk to a 1505.
A side note- Keep in mind that all these radios currently mesh on ~5 GHz and this does not work well at all if you have trees. You will need to have quite a few more access points than you think, possibly as many as 50 per square mile (or more).
Also- The antennas on the 1510 point down, while at least one on the 1522 must point up. This is the 5 GHz one. The other 3 are for 2.4 and only one on the bottom is truly needed (unless you want the MISO (Multiple In Single Out) feature. This antenna sticking up will intrude into the 40 inch clearance required by the electircal code, so you won't be able to mount them as high as you perhaps thought you could. The radio with the cable modem mounts on a strand and has all the antennas pointing down, though.
Of course if you are lucky enough to actually have the power company allow you to mount them on the street lights themselves then pat yourself on the back! In about half of my cases, I have to add another street light arm lower and only for the radio or forget the power pole altogether and put up a metal pole for the radio.
I have learned a lot about outdoor mesh applications and troubleshooting from all my Cisco mesh projects as well as my projects for Earthlink. I was one of the main field engineers for their mesh systems with 300 to 10,000+ radios each. Although they were from a different manufacturer, the basic idea is pretty much the same.
Feel free to ask questions if you want.
