If you have added too much ammonia during a fishless cycle, it wont do any serious harm, but there seems to be some evidence that way too much can inhibit the growth of the bacteria, or alternatively a problem can arise in that your filter media can physically only support so much bacteria, and even with a full colony, it take a long time to get the levels down.
I would therefore recommend a 50% water change (treated water etc etc.) initially, test the levels then do the same again until you get down to about 4-5ppm.
With regards to how much you need to add, then it depends on a number of variables - primarily the concerntration of the ammonia solution you have which can vary from about 5% to 25%, though most common solutions are about 10% concentration.
A 15G UK tank equals about 68l which in turn is 68,000ml
Therefore 1 ppm of 68000ml is 0.068ml, so to get a 5ppm reading you would need to add 0.34ml of pure ammonia.
if your ammonia is at a concentration of 10%, then you should need to add about 3.5ml of ammonia solution. If it was me, then I'd adda bit less, do a test then top up to get to the right levels.
edit: I suggest that you get a small syringe from any chemist to be able to accurately measure the dosage - or if you have kids, then you've probably got one to administer meds when they were babies !
the readings on my tester are off the chart and they havent moved in 48hrs. do you think an 80% water change or something would be a good plan? and how much ammonia do you think i should be adding? drops? 
