Windows Mobile is different from Windows...
Like iOS and macOS for example.
Not a target platform supported by OCPN - ARM is no issue for OCPN: see Raspberries and others from this crowd.
Microsoft is now promoting a UWP (Universal Windows Platform) for their different range of devices in the W10 context.
Programs labeled "legacy" like OCPN can't be migrated that easily.
There are sand box concepts - the OCPN plug-in structure won't work
there for example - and the issue that wxWidgets, the user interface OCPN is using is not ported to the UWP architecture (yet?).
Resuming: no OCPN for a Lumia 550 with W10 mobile.