Not a profitable investment on a 15-year timescale. Potentially profitable over 25 years (according to the linked estimates) - and this is for a project with a

Not a profitable investment on a 15-year timescale. Potentially profitable over 25 years (according to the linked estimates) - and this is for a project with a 50-year concession, with a 50-year extension allowed for. Perhaps it would be silly for private investors to pile in hoping for a short-term return, but over the life of the canal it could potentially be a great investment for sufficiently long-term entities (such as nation states) to invest in.