The effective amount will of course differ greatly between the countries, but please don't forget that the expenses vary as well. (15k a month in Switzerland isn't as much as 15k a month in Germany)
I know a couple of senior (non lead) developers who earn this much.
You can go very very far with that money in western Europe too. Maybe places like Paris or London may be much more expensive, though.
Definitely. In my experience (lead dev in the UK), salaries for senior positions in London are at least 1.5-2x the amount elsewhere in the UK - but living costs are also much higher.
Not true, basic junior devs in Poland start even from $15K per year(invoice equivalent without VAT).
Good devs in Ukraine get $50K/year+ but AFAIK they have 5% taxes only. Good = hireable by S&P500 companies for example. Anyway most of them prefer to move to Poland for example due to better government/QoL.
lolnope