see first of all brain tumor
has Grading rather than staging,. having said patient survive 15 months from diagnosis its reasonable to say that present tumor is of low grade. i suggest to have Brain tumor surgery so called craniotomy
with excision of lesion that debulk lesion from brain and followed by adjuvant radiotherapy+/- chemotherapy(temozolamide) after seeing surgical pathological report. i advise not to give up case and try to do something for him. Suppose patients general condition is poor enough to take treatment then patient can be kept of medical decompression of brain by Corticosteroids
along with INJ Mannitol +/- Liq Glycerol
at home basis.