I have a slightly different take on this.
Don't freely give away your equity.
It's far more precious, and while it feels 'free' (as opposed to salary that really goes out your pocket), I would rather pay the salary if I can afford to. Do you really think that 50% of a tech lead's salary will equate to a 15% stake in the company?
Tech leads are not CTOs.
At least, not yet. Are you paying him 50% of a CTO salary? Unlikely. So give him equity that you'd give a Tech Lead.
Room to grow.
This guy is your first. If things go to plan, you'll probably have many more. By giving him 15%, you are giving away a serious chunk, keeping much less for the possibly dozens or hundreds of people that'll come in. Additionally, if this guy hangs around, he'll want to grow with you. If he does end up being CTO, then at various stages (and there's more than a few) in the journey you will want to offer more equity. Staggering equity like this has many benefits, which I'm sure you'll already know of.
It's a big world...
...and you're just starting up. As you grow, you will meet a lot of great people. Some people will also approach you when they hear about what you do. Some of them may be suitable for the CTO role. Getting someone who's already a CTO, to my mind, is far more efficient than 'growing one of your own'. Not that I want to discourage people from growing into that role... but it can take a long time - something that a startup is always short of. If you hire a CTO soon, you might want to think about what you're going to offer him considering you offer 15% to tech leads.
Don't get me wrong, I am not saying that you shouldn't give equity. I'm saying that equity makes people work harder, feel a sense of ownership, maybe even more tolerant of shifts in business that a startup usually goes through. But you need to be judicious about it. Not stingy. Judicious.
BTW, I think even 1% equity is pretty good. If someone is *asking* for 15%, that just shows me that they are thinking really small, and not too much into the future. I would, in fact, have serious doubts about hiring the guy.
Just my 2p/2c worth. Feel free to comment!