[EPIC] Upgrade go-ethereum to 1.15

[gartnera]

This will be split in 2 parts—a geth upgrade to 1.13, which TAC has built here: TacBuild/go-ethereum#1 and a geth upgrade to 1.15, which we still need to work on.

Tests to ensure compatibility are also required.

[nooomski]

Hey @gartnera, this is definitely on our radar. Can you elaborate which specific functionality you're in need of and why? It would help us understand priorities.

Edit: just saw your thread in Slack, all good!

[vladjdk]

TAC has begun work for upgrading to 1.13: TacBuild/go-ethereum#1