So – upgrading forks (thanks to the STW forum user who sold them to me at a good price!) from QR to Fox 15mm thru-axel. Hubs on existing wheels are DT240s.

I assume all I need is something like this?

http://www.chainreactioncycles.com/us/en/dt-swiss-conversion-kit-15mm-to-9mm-thru-bolt-frt/rp-prod81489?gs=1&utm_source=google&utm_term=&utm_campaign=Chain+Reaction-US-PLA-PLA-All-All-SE-Shopping&utm_medium=base&utm_content=mkwid|sVcQTdJWR_dc|pcrid|68603497608|pkw||pmt||prd|315409US

That’s going the wrong way. You’d fit them to a 15mm hub to let it run on QR forks.

It depends on the hub. If they are the oversize hub it is simply a change of endcap, if not, it is possible with a non-oem kit from USA/ Canada which has very narrow bearing races and a new axle that accept the 15mm QR
https://www.wmsracing.com/wmsweb/AXL15-WMS-15mm-Axle-Conversion-kit-DT-Swiss-240-front-QR-hub-6-bolt-disc.html

One of the problems with DT240s hubs is that they last absolutely forever, so there’s still a load out there that pre-date 15mm QR and 12mm rear or even 10mm becoming succesful. So if you buy used or you have old wheels it’s totally possible that your fronts can’t be adapted with DT parts and you need the kit from jimw, and that your rear needs a new axle to go above 9mm.

So basically what that means is you need to know what you’ve got first. There’s also a 3rd way, the 20mm OS front hub, which adapts to QR, 15 or 20 but uses different incompatible adaptors.

What Jim said