DUBAI, May 26 (Reuters) - Indonesia has mandated HSBCHSBA.L , Standard Chartered STAN.L and CIMB Group Holdings Bhd CIMB.KL to arrange a sovereign sukuk issue of up to $1.5 billion, sources aware of the matter told Reuters on Monday.The head of the Indonesian finance ministry&aposs debt management office, Robert Pakpahan, confirmed that the government had appointed the three banks as underwriters.