Though a main pillar in Lean is testing and learning, the end goal of the framework is to reduce waste. It's good to keep that in mind when thinking about endless possibilities.
In your case specifically, have you established a baseline yet? If not, it would be wasteful to start testing, because without a baseline you don''t even know for sure where (or if) you have issues in your conversion pipeline and therefore you don't know where to begin testing. And again, that is wasteful.
Dave McClure--through his AARRR framework--advocates you should first spend time on activation and retention before moving on to other metrics, like acquisition. I mention this specifically because I'd argue your landing page is part of your activation metric whereas your AdWords campaign is part of your acquistion metric. So, according to McClure, you'll want to spend time improving/testing your landing page before moving on to improving/testing your AdWords campaign.
That said, I'd argue you'll want a baseline of how well your landing page is converting before investing time building an A/B test. If through establishing your baseline you find your landing page is converting at or above industry standards, you won't even need an A/B test for your landing page. If you happen to find this result, you can avoid the waste of building an unnecessary A/B test....
Just a few thoughts--hope they help! Best of luck!