My father has diabetes? T2dm? . Now he takes humalog (insulin lispro) twice per day, each time is 15ml. Is there any better or long acting insulin can be recommended?

Yes. He should be on a long acting Insulin (lantus (insulin glargine) or levemir) along with the humalog. It would be unusual to be on just Humalog unless he is on a mixed Insulin humalog, in which case a long acting Insulin is already in there.