Will that setup allow for an only 15kHz output?
Not only that but you can output any frequency (24khz, 31khz, etc). The main value of going this route is that you get native resolutions of any game
and native refresh rates, so that game speed is accurate (Arcade VGA has a limited set of resolutions and refresh rates). You have a lot of freedom of positioning the screen as well (mostly horizontally). There is of course familiarizing yourself with the software and getting it setup but there are tutorials and once you get it, it's really not hard. There's great support on the sub-forum with the creator of the drivers checking in regularly. I'm happy to help get you setup as well.
The only other consideration is that the Arcade VGA prevents any signal higher than 15khz from being outputted to your screen. I'll assume your screen is 15khz only. The modified drivers that control an AMD card kick in once Windows launches. Prior to that most computers from Bios (prior to Windows taking over), will want to output a 31khz signal. Significant exposure to a 31khz signal for a 15khz tube is not desirable. To get around this, you can:
1.) Wait to turn on your monitor until your computer boots into Windows (only an issue when booting up the computer).
2.) Install modified firmware on the AMD card to force it to send a 15khz signal at boot up like the Arcade VGA does.
There is support for modifying the firmware of the AMD cards, it's through a utility called Atom-15.
Hopefully this makes sense, but let me know if I can clarify further or help in another way.