Is 75 mg of temazepam too much?

Yes: The usual max dose is 30mg.

For what?: The usual dose of temazepam is 7.5 to 30 mg at bedtime, to treat insomnia short term. So 75 mg is 2.5 times the highest recommended dose. There might be other reasons such a high dose is used, but taking this much might indicate an addiction, too. It depends on the situation. Temazepam is not approved for long-term treatment of insomnia.