Bitcoin wallet & 15 chars is not doable in a human life.
By the way your problem is the last '?' character, remove it :
C:\Users\wq\Desktop\hashcat-4.1.0>hashcat64.exe -a 3 -m 11300 wallethash.txt ?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?
Finally hashcat-4.1.0 is outdated. Use v5.1.0
By the way your problem is the last '?' character, remove it :
C:\Users\wq\Desktop\hashcat-4.1.0>hashcat64.exe -a 3 -m 11300 wallethash.txt ?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?
Finally hashcat-4.1.0 is outdated. Use v5.1.0