The loading of the file is very simple, I was having problems with DPPs settings because in fact DPPs (0 to 2) are changed at runtime depending on the ECU coding because of the 3 codeblocks (Manual, Auto & 4x4)...
The default settings to the DPPs are ok to start reversing (DPP0: 0, DPP1: 1, DPP2: 2, DPP3: 3),
then it's easy to change DPP0-2 to point to the codeblock you want to be selected.
(3 pages of 16kb each, so for example set DPP0 to 0x3C if you want the third codeblock to be selected).
At first I was changing every DPP to the values present in the IROM and so having a lot of problems locating anything...
DPP3 it's used for RAM\CAN access so the default value (3) is OK for the entire file.
The 29F400BT flash is mapped @ 0x80000 so loading in IDA you have to put 0x8000 (paragraphs).
I suggest to first locate a RAM variable like dzmNmit (engine rpm) or something like this,
will give you a nice picture of how the system control strategy works.
There are NO direct Maps references in EDC15 due to codeblocks so its a bit tricky to found how they're addressed.
Regarding to the time it takes I worked on this for 2-3 hours for 3-4 days because I've some important & difficult exams to do (I'm a computer science student) and I've very little time to work on this...
I've worked on the PSP modding scene before ("Xplora" is one of my projects) and comparing the two systems the ECU is just a small, easy module (code section is less than 300kb)...
Adding the "overboost" feature & the map switch isn't difficult at all once you have a good picture of the program...