Hi,
Dell E515dn is listed as a supported printer in the About AirPrint article (link provided by LotusPilot).
The E515dn is not a Wi-Fi model, but the printer has an Ethernet port. The AirPrint technology works with both wireless and wired network connections. In this case, you should be able to wire the E515dn (by Ethernet) to one of the LAN ports in the Wi-Fi router used for the iPad's wireless connection. Typically, the wired and wireless sections of a router are bridged, so that the printer and the iPad appear on the same network (subnet).