They probably don't notice that delay, because they are doing something else during that time ... Reading the next ticket, some git admin, replying to an email, checking slack, etc.
As a single example, I don't consider a 15m delay for a full test suite to be a problem. I've got plenty of 5m tasks to do that I can use to fill in that time.
I cannot think of any developer who sits and watches the tests for execute.
I think some developers don't care, and some developers really really care and I haven't found a good way of partitioning the set and focusing on the developers who care.
You need to find the target market where a 15m delay is a pain point i.e. partitioning the set.
I don't personally know of any Devs who consider that a pain point, so it might be a really small target.
Trust me, I am going through the same thing, and I'm constantly questioning whether this yet to be released product has a big enough target market. No good to me if the alpha users comprise the entire target market, so I'm ready to pivot the moment they say "this is great, but we don't have budget/use this less great free thing/can't get approval/will sign up next year/etc".
That's all code for "this isn't a pain point for us."
The uncertain "faster build time" would be nice. But is it worth raising it up and battling for it? Unlikely.
I think a different case can be made if you target the managers instead. "Make developers twice as productive" might be a better selling point.
Compliance, reporting, scaling with number of projects/growth, interop with existing tools, and lastly a good word from other people in the same industry are what's going go sell your product.
In enterprise CI there are a bunch of other tools you're going to be waiting on, and at least from what I've seen on the field companies will run stuff like SCA/SBOM every build and keep a history graph of when and whom added things. The developer themselves typically does not care for that, but the 'enterprise' does
I know personally that waiting 15 minutes for a test suite to finish is super frustrating, but people seem to have normalized it. I've also literally been hired to speed up people's tests, so it's not a problem that doesn't exist. Our current customers are also delighted with the speedups so I know it's a problem. But explaining that problem and why the status quo is bad to developers is especially hard. Btw I don't buy the "developers are immune to advertising" spiel, I actually created some of CircleCIs first ads so I have experience doing this. I just think developers are different and marketing devtools is different again (because of it's not a personal purchase and there are a lot of different stakeholders).