No that amount of change is not normal. You have high myopia which is an abnormal eye not "simple myopia" which is basically a normal eye. I would suggest you start by making sure you are getting your eye care from an Eye MD ophthalmologist, not a non-physician optometrist and certainly not from a commercial change, they really don't care for your eyes as much as your glasses money. I would suggest also you see a retina Eye MD for a baseline examination of your eyes. You are at higher risk of glaucoma, retinal detachment and macular degeneration. We do not understand the genetics of high myopia and there is no way to determine how much myopia you ultimately will have. These is especially true if you are Asian. The world wide epidemic of "near work' has contributed to this (computers, reading, iphones, ipads, video gaming, texting, etc). Also "indoor time" children that are outside a hour/day have less myopia than kids that rarely go outside. You also need to avoid eye trauma, contact sports and amusement thrill rides that bang the body around.
I don’t know where you are reading that about glaucoma but virtually everything you said is incorrect. Most people with glaucoma do not go blind or have bad vision. Most people that do go blind or have bad vision either were not diagnosed until the glaucoma was far advanced or do not use their mediciations and/or keep their appointments with their ophthalmologist. Probably fewer than 1-2% of people with glaucoma need surgery. Glaucoma surgery using the MIGS techniques has high success.