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.
If...
more... 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.