Can I stop Invisalign because it is taking a lot longer than anticipated?

I'm 27 years old and currently wearing Invisalign for 2 years (50 trays). After 50 trays, my dentist said my teeth weren't ready and ordered more trays. They came in today and I found out there are 43 extra trays and I will need MORE buttons on my teeth. I don't think I can withstand Invisalign for another 2 years. I want to know if it is alright to ask my Dentist to shave my attachments off and stop my treatment. Also, is it common to have Invisalign or braces last for almost 4 years?