I just bought a DAP-1522 to use with my DIR-815 as I had used the earlier version previously with a DIR-655 successfully for about 5 years.
It took me several hours to get the set up to work. I began by trying WPS both just using the PBC and by logging into the admin screen and triggering there. Both worked in terms of successfully connecting the devices to each other but neither allowed me to connect to the internet through the 1522. I tried both bridge and AP modes. I wanted to use mine as a bridge ultimately, so my switch was in bridge mode when I ran through these next steps.
I'm running firmware versions: 1.01 on the 815 and 2.02 on the 1522.
What worked for me was to completely reset my DIR-815 (I had a bunch of reserved DHCP addresses but many were old so it was good housekeeping for me) and also reset the DAP-1522, so both were running default out-of-the-box settings from DLink.
Once this was done, I used WPS PBC mode from the admin console of the DIR-815. It worked within 15 or 20 seconds, and I was then able to see that the WPS connection had worked and it had set up a new SSID for the network and also a very long network key within the admin console of the 815.
I verified that I could hit the internet from a laptop that I connected via ethernet cable to the DAP-1522. I had to turn off my wi-fi radio to get the laptop to use the ethernet card by default. I also did this so I knew any signal was coming through the 1522.
Once that was done I unplugged the DAP-1522 and moved it to my media center and connected my PS3 and ran the network setup for the PS3 in easy mode. It detected the device, and pulled an IP.
The final thing to do is was to change the SSID (Wireless Network Name) and the network key back to something more usable, because by default the WPS setup had assigned a 64 digit alphanumeric string and also a funky SSID.
I had to log into the DIR-815 admin console -> wireless settings -> manual wireless connection set up and change the SSID and network key for both radios (2.4GHz and 5GHz).
Then I logged into the DAP-1522 using my ethernet cable and laptop, and changed the SSID and network key there to match. SSID can be different, but mine matches the DIR-815 since it's not broadcasting from bridge mode, I don't care.
I rebooted both devices after making these changes and everything worked great and is working great.
I've attached other tablets and laptops via wi-fi, and also reserved some IPs in the 815 without issue.
Hope others find this useful.