IMO I think its too long. If you look at the correlation of how long engagements are, and the rate of divorces, it gets higher and higher the longer the engagement is drawn out (specifically it starts to get high after 18 months+ of an engagement). Just something to think about.
That won’t much of a concern once you get engaged it will
help you keep more involved into each other and also it would help you prepare
for your future planning about what needs and not needs to be done.
FH and I will have been engaged for 3 years and 8 months when we get married October 3rd 2014. I am happy that we did it this way, we got to plan the wedding that we wanted and not the one we could afford. That of course wasn't the only reason, we were also in a car accident that pushed back our wedding quite a bit.
But as for the long engagement, don't let anyone tell you that it is wrong. You can be engaged for as short or as long as you want and there will always be someone who will share their negative opinion.
If you are going to be engaged for so long, enjoy the relaxing process. Decided on the things that you like and the styles that you want. Compose a plan and then when it comes time to book you are ahead of the game!