cgjimeneza, sorry to say that you have no chance to install the mod without reinstalling SH4.
This is the negative point of the operation, the positive point is deinstalling your stock version of SH4 has no implications on your modded installations.
Deinstall Stock 1.5, install 1.0 and update to 1.4. Make a copy of clean 1.4 to your modfolder (if you like keep this clean 1.4 and take a second copy for the FOTRS Mod) and when ready update the stock game to 1.5.
If you do this you go exactly the way i did 2 month ago. There is only a stock installation in my C:\Programs\... All my Mod copies are in my C:\Games folder. And after having watched a hard working HD you will be like me the proud owner of 45 GIGABYTE Silent Hunter 4 in 2 clean installs and 7 Mod folders each round about of 5 GB. :rotfl::rotfl::rotfl::rotfl: