Unable to find any PTR-records for the specified domain/ip :(
Log
+000
Resolving PTR record of '15.221.164.0'
+172
ERRNo PTR record availible DNS server 'x4.amazonaws.org' raised an NotExistentDomain error, while beeing queried for PTR-records on domain '0.164.221.15.in-addr.arpa'.