I was wondering if anyone knew if the 6 speed manual transmission from the 2015 fit will bolt onto the 2008 fits motor without much modification I am going to need a new transmission soon and I'd like a 6speed

 

I don't know how readily the 6 speed can be adapted to the 1st generation (or 2nd generation) Fits.

However, I hope you realize that the extra gear ratio will not affect your cruising RPMs. The 6th gear ratio (taking into account the final drive ratio) ends up being essentially unchanged from the 5th gear on the older Fits. All you get with the extra gear is more rowing when you're driving around town and perhaps slightly faster acceleration if you push things to the limit. I personally don't consider those an advantage.

 

^^ X2 on the final drive (cruising RPM)

Plus, the tranny would EX$PEN$IVE as you would be dealing with new parts... it's not like you could find a '15 unit in a junkyard yet...