Transaction fee too low - transaction gets not confirmed

[NiKrause]

when broadcasting a multisig transaction (and maybe others) the calculation of fees seems insufficient.

1. How are the fees calculated?
2. Do we get correct fee estimation (sat/byte) from Electrumx or from somewhere else (Coingecko) ?
3. Can we optimize the fees accordingly?

[davidreband]

networkTransactionFees.ts
return new NetworkTransactionFee(response.fast + 15, response.medium + 12, response.slow);