It makes sense to have a look at revising the slot of 16585/86 or facilitating an RSA with Vasco Exp to find a more optimum schedule for it. As it stands, there is scope to slot in one more train between 16511/12 and Panchaganga.
16515/16 has the same 14 coaches as Panchaganga, and the difference of 3 hrs in runtime end-to-end is definitely not doing it justice. Certain stops upto Hassan could be reassigned to 11311/12.
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Currently a higher portion of travelers in 16515/16 come from Mangalore due to the reasons you've touched upon, but SR would not receive it at MAQ instead of MAJN (the Madgaon MEMU and SBHR Passenger have more privilege). If SWR expect more patronage from coastal Karnataka, the train should be speeded up and given a daily run bypassing Mangalore while an early morning Vande Bharat from Bangalore departing ahead of 16515 and returning behind 16516 would be a good deal for Mangalore.
And there is sill room for another non-premium daytime train. With 2 rakes, Gomteshwara can run daily taking the timings of 16540 and making a late night return to MAQ.
For these bypassing trains, Farangipet station should indeed be developed by SWR. In fact they could have operated Padil station like Thokur instead of handing it over to SR who have decommissioned it for detaining freight trains.