I have a 2i2 I use to carry around when needed.
We also have a couple 18i20s when in our usual locations.
Make sure, as Teunis noted, to have the ASIO driver for the Focusrite selected.
If that causes other problems, it's OK, those are fixable too. Stick to it & proceed down the path of getting it set up right, you'll be happier in the long run.

Also make sure your monitors or headphones are using the Focusrite out, not the computer out.
That physical connection on the computer is tied to system drivers that will cause this problem. Even though Reaper may show correct drivers, as soon as you connect to the internal card you've introduced a likely problem. OS routing won't show in Reaper.
In this scenario, Reaper would be sending a proper signal back to the Focusrite, but the OS has tapped it along the way and is adding latency from the onboard device drivers. Eliminate those.

Make your sound your own!
.. I do not work here, but the benefits are still awesome