I'm sorry Georg, that's just not true. Mirtazapine is one of the better ADs out there—that's not my opinion, that's a medical fact. If you had a bad experience with it, then it's totally understandable that you'd feel that way, but the vast majority of people who take mirtazpaine love it. Saying "it only gets worse the longer you take it" and "better don't touch it at all" is just going to further frighten people that are already dealing with depression and anxiety and are scared and vulnerable in the first place.
I quit mirtazapine cold turkey 7 weeks ago after taking 45mg for 12 years and it was a walk in the park compared to quitting Paxil more than a decade ago. SSRIs are generally harder to taper off of. Just because it was easier for me doesn't mean it will be easier for everyone, of course.
Mirtazpaine isn't right for some people, of course. But that doesn't mean you shouldn't give it a try. Especially if you have anxiety and insomnia.
Tess, I wouldn't recommend messing with the dosages set by your doctor. Although, I'm now questioning your doctor's knowledge of mirtazapine if he told you to cut 15mg in half so it wouldn't be as sedating. That may be true with some ADs but not mirtazpaine: it is more and more sedating the more you lower the dose. (To a point—it's not like if you take 1mg you'll sleep for a year or anything.) But 7.5mg is more sedating than 15mg, in fact, at 7.5mg it's just a sleeping pill with antihistamine properties that won't do anything for depression whatsoever.
It's not until you get up to 30mg or even better, 45mg, that it becomes much less sedating, begins to combat depression, and you can function well on it.
Are you on any other meds at the moment? Or did you just quit another med before you began mirtazapine? Are you taking tramadol or St John's Wort or opioids for pain or drinking any alcohol? (I'm a wine freak, and one drink while taking mirtazapine felt like 3 drinks, to me. Which was a problem when I just wanted wine with dinner and had no desire to feel completely loaded at 8pm on a Tuesday LOL.)
And yes after 3 days it's totally fine to stop. Especially at that crazy-low dose. It takes time for these meds to work so I'd say don't give up after only 3 days. Everyone goes through that adjustment period and it, more often than not, improves dramatically and you feel completely normal again.
Keep us posted and good luck!