Add Rapid with Increment to the Quickplay Buttons

That is a nice thing to consider, actually!

5+3 is 420/480 (move 40/60)
20+10 is 1600/1800 (assuming 20+10 gets implemented, but 15+15 is 1500/1800, so not a huge difference anyhow)

------ Middle of these two would be 1010/1140

To remind you, these were the two main suggestions:
10+5: 800 / 900
15+5: 1100 / 1200

So 15+5 would also fit the "Slowish chess with Increment" 'spread' a good bit better than 10+5, not just the "Rapid" one..
.. In theory.
In practice, as I mentioned above, how much Increment we got probably doesn't matter a massive deal; but you still have to plan for 30minutes+ (just like for 15+15), as opposed to 20+ (for 10+5) or 10+ (for 5+3).

In that sense, 10+5 indeed fits a lot better, as "Slow chess with Increment, but not too slow"
In particular if we ignore 5+3 altogether (which in the end is still Blitz), and say eg that the Range of Slowchess-with-Increment starts at 10+2, and realistically ends at 25+15, we get something like this for a spread:

10+2: 680/720 - 25+15: 2100/2400; so 680-2100 move 40 wise
With 20+10 we'd have something on the high end (1600), and thus should also get something on the lower end of the spectrum, at ~900 or so ideally; 1100 is a bit far up.

So ya, guess I'm coming around to 10+5 :)

I agree with all the other people asking for 10 + 5
Let's get it done!
If I could have a second ask, it would be to replace 5+3 with 5+5. I always play 5+5 custom and almost never have to wait very long to get a game so I know it must be quite popular even with no quick button. And +5 increment when in time scrambles is much more civilized and comfortable than +3.

5+5 is Rapid again, so that's not gonna happen. Let the Blitzers keep their slow Blitz ;)

It doesn't really matter what you call it, rapid or blitz, it's only a name. And the extra two seconds are not going to make the game that much longer, but MUCH more playable in time scrambles. So we'll have to disagree about that but I want to stay focused on the fact that 10+5 is very deserving for a quick pair button.

Are there really people who prefer 10+0 to 10+5 or similar ? I understand that for short time controls ( < 3+0 ) no increment is a thing but imo the only good reason to play slower time controls without increment or delay is for over the board tournaments in a club that still has analog clocks.

I would prefer some more rapid options like 15+2 or something along those lines. But the appeal for some @erikelrojo may be that they still have the option to play for time if the position falls apart. I would of course like to eliminate that nonsense from my games but I have been guilty of that approach as well. That being said, Classical 15+15 is just too much increment in my opinion.

I also think we should remove the custom button and add 10+5 or 15+5 rapid time control!

+1 to removing custom button and adding 10+5 or 15+5

@erikelrojo So true. You set aside that much of your time to sit down and have a serious game and then what? to have it end in the sillyness of bumbling around to see who can move their pieces faster when it gets down to seconds on the clock? The two just don't go together.
I don't mind having a 10 0 button though if some people still want to play that but it will be interesting to see when the 10 5 is there how much less people use the 10 0.