Ngl upgrading the walls doesn't matter much, I'd usually just upgrade my walls when everything else is maxed or I need to waste some gold/elixir. Most people either use air attacks or root riders nowadays and siege machines just destroy them 😂
For those who dont know after the lastest update before halloween the loot thing was updated and now u get more loot before in th12 i was getting 600k now its 1.5m
sorry to break the news to you but, it was confirmed that the cannons / archer towers are required to be merged to upgrade to th17. So you wont be able to get to th17 unless you have 4 archer towers and 4 cannons to lvl 21.