Civ VI had a higher base
And it isnt a 56% increase, the game has reached 11.8k less than one month ago (July 27th)
I stand by my opinion, less than 15k would be a big issue IMHO
11,758 to 15,000 is still ridiculous. That's a 28% increase, Civ VI never received an increase that big in its first year, maybe ever excluding the release of a major expansion pack.
The highest increase in peak concurrent players week to week CIV VI had was 26% (9,317 raw number) during the 2016 Christmas Holidays while it was on sale for 10% and received the Winter 2016 update. So the holidays, a sale & an update couldn't hit 28%.
The second highest was 24% (5,855 raw number) after the Summer Update in July 2017 plus it was on sale for 33% at that time. The biggest increase (in the first year) solely from a sale was June 2017 when it was on sale 40% off. That was a 21% increase (4,568 raw number).
On Sunday, VII peaked at 9,595. To get to 15,000 it would have to increase it's numbers by 56% (5,405 raw number). We can all agree that is ridiculous to expect and won't happen.
You said about the 11,758 number, that was after the 1.2.3 update which brought players back. Again, that'd still be a 28% increase (3,242 raw number). There is no update this time, just the 30% sale.
The biggest week-to-week increase for VII so far in terms of peak concurrent players for the week was 23% (2,252 raw number) after the huge 1.2.2 update, plus it was on sale for 15%. So even to go from 11,758 to 15,000 (3,242 raw number) would be ridiculous.
If there was a big update this week as well as the 30% sale, then I think we'd see a big increase of around 25% which would put the raw number to around 12,000.
As there is no update, my prediction (could be completely wrong) is it'll peak somewhere between 10,000 & 10,500 - maybe up to 11,000. 100% won't be 15,000 and should never expect that.
You can stand by your opinion, it 100% will not hit 15,000 and it will not be an issue in the slightest.