Sir, Answer for 16515/16 Query is exactly in your first para itself - Bypass. Anything entering Mangalore Central or Mangalore Jn. would mean lots of time consumption due to Huge yards + Zonal Changeover point from SWR to SR & SR to KR & other formalities like Reversal/Attachment/Detachment, Checks, switch lines & turnouts speed etc. Udupi & Specially Uttara Kannada People least prefer because of Huge runtime & late arrival at enroute stations in KR due to least priority. Few from Udupi District do get down at Bantawala/Kabakaputtur & switchover to Buses to reach Home earlier then train.

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16515/16 would run via Padil Bypass, would definitely attract many takers from Coastal Districts of Udupi & Uttara Kannada. But that would also mean Mangalore people would lose Day Bangalore connection.

For 16515 towards Karwar, There are 3 trains ahead of it. 12134, 12620 & 10108 MEMU.

For 16516 towards Mangalore direction, 10107 MEMU stays exactly like 1or 2 block stations ahead.

If bypassed, 16515/16 Day train can be proposed to extended upto Madgaon or even Vasco if SWR agrees, No harm in that. This would also mean Vasco, Madgaon to get daily Intercity Day connectivity to Blore, South KR & Udupi, Mookambika, Subramanya, Dharmastala, Sravanbelagola & other Religious & tourist places.

Vande Bharat introduction between Bangalore & Mangalore is thought off, once Ghat section gets Electrified. They can think of bypassing 16515/16, taking opinion from All Rail Associations from Region into consideration.

There is a Abandoned 'Farangipete' Halt station within SWR limits nearby Padil bypass cabin/Mangalore Jn. & has Good Highway connectivity, just 50~100 mts from Tracks. SWR can develop it as Block station with All Good amenities, So that Mangalore people can still hop on/off all trains bypassing Mangalore area if any in future.

Your opinion about Talguppa holds good. Almost Decade back, when Panchganga was non-existent & 16523/24 were running, Myself commuting to Blore from Kumta use to go to Talguppa & take 16228 to reach Blore faster & vice~versa. Even People from Byndoor/Kundapur taluks would do same.

Regarding connecting train to 16511, My opinion would be better to swap slots of 16511 with 16585, such that 16585 starts early from Blore take 16511 slot from Hassan, arrive early at Mlore & leave early towards Murudeshwar. That would also mean early arrival at Murudeshwar &...
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possible extension till Karwar or even till Madgaon/Vasco.

Few Coastal rail users association also suggesting Rlys to find if it is technical feasible to carry out RSA with 17309/10 Vasco Exp. Incoming Vasco Exp from Yesvantpur can leave as Vasco - SMVT Exp via Karwar & SMVT-Vasco would leave as Vasco-Yesvantpur same Night. PM can be taken either at Vasco or SMVT, making pitline free at another end.

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.