14 years is a very long time to take Ambien! We usually ask our patients to take it for the shortest possible duration may be few weeks.
There are no studies or literature regarding long term use of Ambien (Zolpidem) so it is very difficult to comment upon the long term side effects but as you are taking this medicine since last 14 years without any problem so apparently there may not be any significant side effect.
It is a very good idea to taper down Ambien but it is going to be difficult for you.
This medicine should be taper down slowly and then stopped to avoid withdrawal symptoms. It is for sure that you are dependent on this medicine and tapering down 30 mg is not going to be very easy in your case.
First of all you should do it under the supervision of your doctor / psychiatrist.
There can be two possible method by which this medicine can be taper down.
1 - By reducing the dose of Ambien gradually for example by reducing say 2.5 or 5 mg every week till a patient is able to stop it completely.
2) Shifting the patient on a long acting benzodiazepine such as Clonazepam and then slowly taper it down.
In any case, whichever method you follow it should be done only under supervision of a doctor otherwise you can experience withdrawal symptoms and or rebound of insomnia
I hope this helps, please feel free to discuss further if you have any related query.