The sourcing is a bit dubious, but let's roll with it because it does make sense. And if common sense and dubious Twitter sources can't be right, then I don't want to be wrong.
The biggest problem isn't that the picture, say, is perhaps fake -- it's a standard dressing room shot that you so often see from tours of Stamford Bridge -- it's just that I cannot find the actual original. Two Twitter accounts (@TheChelseaViews and @FootballFact101) with large number of followers are basically responsible for its spread through the network, but I doubt either of them are the primary source. This account may have been the first one to tweet it, but it's again unclear whether the picture is actually his.
Further anecdotal evidence comes from another Twitter user, after a scouting trip to the Megastore at the Bridge.
Yet, even if Twitter is wrong, there is plenty of common sense in Drogba taking the 15 shirt.
Suddenly, the somewhat random switch from #15 to #17 for young Mo Salah a few days ago makes so much more sense! As much as there may be some Hazardian magic in the 17 shirt, a few eyebrows had been raised when his preferred #22 stayed with Willian. Turns out that he was just making room The Return of the King!
When Drogba first joined Chelsea, he chose to wear #15, with his preference (and number at both Marseille and for the Ivory Coast) belonging to Damien Duff at the time, in that fine English tradition of giving the left winger the #11 shirt. After Duff left the club at the end of the 2005-06 season, Didier switched to his now iconic number, and while that number now belongs firmly to Brazil's Oscar, Chelsea have never not won the Premier League with Drogba wearing 15... so they might as well just give us the trophy for this season as well.
It is, after all, written in the stars.