Mirtazapine for insomnia - is 15mg not enough?

The doctors I work with say the lower dose (7.5 mg) is more sedating than a higher dose. Perhaps you need to go down rather than up?

Hi, Mink!
It's true that it can take longer to fully treat depression/anxiety but you're right about sleep. It's prescribed at low doses for the side effect in this case of causing drowsiness/sedation and should work immediately.
Everybody responds differently to this type of medication so there's no set dose that's effective for everyone. You should probably talk to your doctor and explain that this dose isn't working for you. It's possible that a dosage adjustment might be in order.
Best regards and I hope you'll be getting your Zzzz's very soon.