Exactly, if you have CPL you need to fly 25 hours, but if you have an IR+NVFR, you can do it in 15.
Basically, an ICAO CPL will be converted in EASA PPL and then add a CPL crediting the experience you already have. (at least 150 TT)
For the theory... I think you will have to redo all the 14 subjects here.