Is temazepam 120-150 mg too much for a first time user?

Too much. Never more than 15-30mg per day. The dose you mentioned is just way too much!
Temazepam. Temazepam comes in 7.5mg, 15mg, 22.5mg and 30mg. Yes, 120-150mg is way too much! do not even think about taking this medication without consulting your physician. It is dangerous, and should be given only after a full evaluation by your physician to determine whether it is appropriate for you.