My wife has been prescribed 30000 iu vitamin d3 for delusional activity. is this better treatment than atypical antipsychotic medicine?

Who knows: There is some limited information that vitamin d deficiency may be linked to certain psychiatric problems like delusions, however, since it isn't the only cause, i would not advise stopping her current mediation without talking with your doctor. Is her d level low? 30000 units is a very high dose of vitamin d. How often is she supposed to take that dose? Once or twice a month is ok.

No, not "better": If your wife has delusional activity, she needs to be seen and treated by a psychiatrist -- who may well prescribe atypical antipsychotic medicines. Vitamin d deficiency has known relationship to depression, but not necessarily delusional disorders. If she is very deficient by blood levels, 30, 000 iu could be reasonable temporarily. I would see replacement as only part of her treatment.