Theoretically they dont need changing until atleast 60k
The issue is that they are recommended on the service schedule to be changed at the 6year/60k service so yes, despite not needing a change, probably best to do it anyway.
Our IS300h was a low mileage car and had 20k on when it got to 6 years. Luckily at that point in time Lexus Essential Care existed, so I just opted for the major service and no spark plugs as theyre an extra £150 on that particular scheme. Unfortunately, they got rid of the essential care now