Discontinuous stays in UK

Hello,

I am switching employers and having to renew my VISA from Tier 2 General to the new Skilled Worker Visa. The application asks 'How long have you lived in the UK?'
Does this mean my most recent residency in the UK on my current visa? Or could it include previous stays?

I have been on two student visas in the past: 2015-17, 2017-2018 with a period in between where I lived and worked back in the USA. I then returned to the UK in 2019 on a Tier 2 Visa.

As there is no way to specify these discontinuities in the application, my question is whether, for the purposes of this application, I have lived in the UK since 2015 or since 2019?

I would be hugely grateful for any insight!

Most recent stay since returning.

Thank you!