Throttling got better with every revision of the XPS 15 that I had. On 9550 it was abysmal - sudden downclocks to 800 Mhz, mouse cursor starting to lag and making the laptop unusable. On 9560 it got mostly fine, with occasional downclocks to 800 Mhz, but much less frequent. With my current 9570 it's all good, I can use it on any charger starting from 45 watts and it's working fine.
