I may be in the minority here, but I think the Bx15 needs to be split.
One idea I had was to make the Hub - Manhattanville portion into it's own route and leave the Hub - Fordham Plaza as the Bx15. I was gonna say extend the former to Wakefield-241, but I realized it wouldn't work because of the . So I figured, why not send it to Pelham Bay?
We can call it the Bx61.
Here's the routing:
Normal route to the Hub
Right on 149th Street
Left on Prospect, then go up to 160th
Right on the fork onto Westchester Av.
Left on Hoe Ave, then a right onto West Farms
At West Farms Square, right onto East Tremont
Left onto Morris Park Ave then continue until Eastchester
Left on Eastchester
Right on Stillwell
Then when it gets to Pelham Pkwy, it follows the Bx12 to Pelham Bay.
This is my first proposal so any feedback is welcome.