The 2 digit code 15 indicates loss of RykoNet to the PLC node on the machine. It can indicate that either the CAW IV or the coinbox are offline, or both. If you look at the PLC node in the carwash control cabinet (small green box), do you you have a red, or green LED light. If red, it indicates the PLC node isn't communicating with the PLC itself (bad node or cable). If it's green, but it flashes 3 times every 5 seconds, this indicates it isn't detecting the CAW IV.
Did your site take a direct hit through your POS system? If so, it's quite possible it could have damaged the CAW. If you have an original style CAW IV (white box about 10" x 10"), it's possible that RykoNet could have shut off if it lost it's programming. If it's a newer model CAW IV iC or Site Server style, that option isn't there as they are all RykoNet arming.
Go into the diagnostics screens on the CAW and see if it passes a network communications test and if it can see the PLC. If so, it may be that you just need to put your run/stop switch to stop, then back to run. On some occasions though, it may require using an HPP to reset a bit to get it to clear.