upgrade dlp 14.0.1 to 15.1

we have a three tier DLP 14.0.1 

1. can i upgrade symantec dlp 14.0.1 straight to 15.1 or i have to go for 15.0 first then 15.1 ?

2. and is it necessary to upgrade the Oracle DB too ?

3. do i need upgrade anything else  (agents, any feature besides detection and enforce) like the mail prevent or else ?

sorry im very new to this, and is there any arcticle about backing up all of it (enforce, db etc) for this process ? 

i found the easy way for upgrading the dlp on youtube but it was a single tier...and it says manually ..https://www.youtube.com/watch?v=rEAYQQTB0DY

is there any video for three tier ? :)

regards,

Dwi