The way I see it, 30ips was born of the need to get decent signal-to-noise performance out of narrow track widths on multitrack tape machines. When multitracking a piece of modern music in the studio, it doesn't matter that a 10 1/2" reel only provides 15mins playing time - in fact that's comfortably more than what's usually needed. Any compromise to the low end can be tuned out with signal processing, of which there's usually a lot done anyway, when making a studio recording of modern music.
For high-quality two-track use 15ips is a better proposition as it does not involve a trade-off at the low frequency end, and each reel provides double the playing time.
If you want an improvement in two-track performance, in my humble opinion it's better to go to wider tape than to 30ips. Going from 1/4" to 1/2" tape or from 1/2" to 1" offers a bigger benefit in signal-to-noise than going from 15ips to 30ips, because the tape noise drops without the increase in the bias noise which is a consequence of the higher speed. The improvement in signal-to-noise from wider tape also does not come at the price of a deterioration at the low frequency end. The running costs again increase, as with going to 30ips, but each reel provides the same playing time. And the wider tape also provides more stable azimuth and is more stable in storage. Of course you need to change heads, head blocks, guides and so on - or obtain a machine set up for wider tape in the first place. That, of course, costs money. But if you see cost as an issue, for two-track use, you're better off sticking with 1/4" tape at 15ips in my opinion.
With best regards,