I was always told that heavier corrections (I have about -10 dioptrics) were tricky because they would have to laser away to much of your eyes' "back wall". This would make the eye structure weaker which could result in eye deformation (bulging eyes?). Truth to be told: that sounded possible and scary enough so I didn't investigate further. I'm ready to be proven wrong :)
I think the answer to the question is that it depends on how thick your cornea are, and how far the surgeon is willing to push it. Some surgeons are more comfortable working with thinner margins of error than others. You want a doctor that is conservative on this metric. I would go in and get a (free) scan to find out whether or not you're a good candidate.
Also heavier correction gives not as precise results as small corrections : it depends of the cicatrisation of the eye. You might end up having a better vision but still requiring to have glasses.
It seems there exists alternatives like putting a lens inside the eyes which gives really good results and is also reversible. The lens is visible if you look closely. I didn't try the method though.