Re-write in Cake3. We recently upgraded our app from 2x to 3x. 3x is a new architecture altogether… Bye bye arrays and welcome objects 
combine with hhvm or php7… which makes it ridiculously faster!!!
Upgrading our 8k LOC code took nearly 50 hours combined (all devs) but was it worth? Absolutely YES!
Bottomline: Learn the Cake3 stuff and then upgrade - one controller at a time.
I use Sublime Text 3, which made my work twice as fast (as compared to my colleague who uses Netbeans)…
Happy upgrading