That is the way it works with ENCs, (aka vector charts). The SENC files need to be built once, on first viewing. Thereafter, those charts
are ready for immediate load.
You may be happier with raster charts
(NOAA RNCs), at least in the US. NOAA ENCs are tough to work
with, and are not really designed for the types of places that most cruisers find themselves. They are designed mainly for big ships entering major ports