"a) It is said that if a tick bits you, you might get the lyme disease. Is it possible that it bit me (it was only inside my leg)and how do i find out 15 years later?"
yes, the most common way to aquire lyme disease is from the bite of a "deer tick". it is IMPOSSIBLE to find out 15 years later if you were bitten by that tick or if that tick was a deer tick. the only thing you could do is have a battery of tests to try and figure out if you have lyme disease.
"b) Is it possible that the above vision symptoms are caused by lyme disease?"
yes, possible
"c)I didn't mentioned and i don't know whether it is important, that since a few months I feel a little vertigo and sometimes wake up in the night with a feeling of earthquake. Does it has any conection with lyme disease?"
yes, possibly
I don't think that you have Lyme disease only because you did not exhibit any of the typical symptoms of the disease following the tick bite. Also, since the tick was taken out immediately it is unlikely to have caused lyme disease. Did you experience fever, rash, headaches, and/or fatigue? If not, you most likely do not have lyme disease.
Your visual symptoms do not sound terribly troubling (they may be troubling to you) but they seem actually quite normal. Flickering when looking at the sky is NORMAL. EVERYONE experiences this. This is a normal function of the retina. There is a name for this but it eludes me right now. Snow in low light is also normal. At least it is for me and I asked my husband who also confirms that in low light settings everything appears like snow or like a static channel on TV but less white and obvious (if that makes any sense).
As far as scotomas, you would have to get your eyes dilated to see if there are any retinal holes, Weiss rings or other things that can cause scotomas. Sometimes this is just your eye adjusting to light/dark and sometimes it is caused by an underlying problem. There is no cure for scotomas but it would be a good idea just to get it checked out (it can't hurt) with a simple eye dilation examination. If there is a retinal tear or optic nerve problem, the doctor will be able to see it and it could prevent any future vision issues. However, most of the time scotomas are benign. Annoying but not harmful.
As far as the vertigo goes, do you mean that everything is literally spinning? There are so many things that can cause this that it would be difficult to give you an answer as to its cause. Go to the doctor and they will take blood tests to make sure you are not anemic or vitamin deficient. I know vitamin b12 deficiency can cause this sensation. Other things that can cause vertigo include inner ear infection, viral infection affecting the middle ear, stress or anxiety, high or low blood pressure, diabetes, Benign Positional Vertigo... The list could go on and on. I’m not sure about the earthquake feeling although I have woken up feeling "shaky" before. In my case, I think its stress and lack of sleep or strange sleeping patterns.
The effect you see when you stare at the sky is called Scheerer's phenomenon or blue field entopic phenomenon.