There is a nifty tool for comparing features between releases:
Personally, I went ahead and installed the JTAC recommendation 2 days ago on my home SRX300 for testing before using this for customer devices and came across a few problems. (from 15.1X49-D170.4 to 18.2R3-S1.7)
set interface ge-0/0/0 unit 0 family inet dhcp-client
is not a valid command anymore, this is changed to:
set interface ge-0/0/0 unit 0 family inet dhcp
Also, updating remotely and using the root user, i was locked out becuase i was missing the following:
set system services ssh root-login allow
These are relatively minor issues, but it would have been nice to know these in advance and i'm not sure what the best way is to get up to speed to these type of changes between 15.1X49 and 18.2R3
Also with the JTAC recommended 18.2R3-S1.7 and a zeroized config (after the update), DHCP-server doesn't seem to be working, which i'm still troubleshooting.
Because of these issues (having to use a console cable to allow ssh root access and my DHCP breaking) i'm holding off on rolling this out on customer firewalls, who knows what more issues there will be in more complex configurations.