High myopia of -7 for 2 yr, is there is any chance of retinal detachment? after how much time complications of high myopia generally arises?

Myopia: Most likely were born with the genetics that resulted in myopia. If do the you are at a slight increase risk for retinal detachment. Maybe 1/5000 instead of 1/8000. So all eyes are at risk, with myopia the retina is slightly thinner resulting in a slightly higher risk for a tear that could result in a detachment. Any sudden bright flashes, burst of floaters, or a curtain or veil over your vision.

No time limit: High myopia has a life long risk of retinal detachment that is higher with personal history of retinal tear or detachment in either eye, the presence of retinal lattice degeneration, family history, the development of a posterior vitreous detachment and with cataract surgery. The last two 'events' occur with age. Risk is present throughout life and as a patient ages. Go to eyemd with symptoms.