How long does vision take to stabilize after LASIK?

1 week is very early in the healing process, so it is not uncommon for there to be fluctuating vision. Sometimes patients are asymptomatic for dryness, yet their vision can still be affected. It is definitely possible for the vision to return to 20/15, but it is not guaranteed. I would use lubricating eye drops aggressively and follow up with your doctor. 

It sounds like you are experiencing a very normal healing pattern.  You may return to 20/15- but the truth is that no person can truly predict that.  Although you don't feel that your eyes are dry, more than likely you have a greater degree of dryness now than you did the week before surgery, and it is likely greater than you will experience in months to come.  I tell my LASIK patients that we expect a truly stable prescription 3-6 months after surgery, but most of them will feel stable at 3-4 weeks.  My advice to you is not to worry too much about the visual acuities (20/15 vs. 20/25, etc.)  Just focus on independence from glasses and contact lenses, and take care of your eyes by following your doctor's drop protocol.   Congrats on your new vision!