Could be all or none of the things you mentioned, Doodles. Here's what I'd do: in your windows control panel, choose the most resource efficient settings (memory saving and power saving features). Then when the time comes to record, unplug all unused devices, and close all unused programs. If you really want to be sure, reboot the computer before you begin.
If you still have lag, you could try reinstalling the audio interface drivers. Always make sure your computer is virus-free, and periodically run malware bytes (anti malware). It's free
https://www.malwarebytes.org/ and really good. For best results, run it in safe mode (to do this switch off your computer, then when you switch it back on, tap F8 repeatedly while it's booting until a black screen with a text menu appears. Choose safe mode with the arrow keys and press enter. Then run malwarebytes. When it's finished, reboot.
If you _still_ have lag, post again. I'm pretty sure your system specs should be able to cope with a bit of audio recording.