KARACHI, April 22 (Reuters) - Pakistans foreign exchange reserves were flat at $15.05 billion in the week ending on April 17, unchanged from the previous week, the central bank said on Thursday. Reserves held by the State Bank of Pakistan (SBP) fell to $11.11 billion from $11.16 billion a week earlier, while those held by commercial banks rose to $3.94 billion from $3.89 billion, said the SBPs chief spokesman, Syed Wasimuddin.