You can install it with 10.3 payload by selecting 10.3.0-28J in the installer.
If the installer doesn't allow you to select 10.3, Get the otherapp payload from
here, then use the
offline installer. Place the payload named payload.bin in the installer's folder, and it should install the 10.3 payload in your oot3dhax
(Another method would be to get the 10.3 payload for your region, and use svdt to delete the payload.bin from the cartridge, and copy over the 10.3 payload.bin, which would do the same thing.)
Do keep in mind, though, that oot3dhax has historically been rather unstable, so it's also possible that 2.5 payloads and 10.3J don't work well together, and that would lock you out of homebrew if you updated and it wasn't working. I'd suggest looking around and asking to see if people have it working on the same 3DS version as you before really updating.
(
Here is probably a good place to ask.)