Regrettably, it might be attributed to various factors, and the potential explanations are numerous without direct observation.
It may be crank pressure.
It is possible that with only 1.5 litres of oil in the vehicle, the oil in the turbocharger has been degraded, resulting in a blockage of the drain line.
The unlubricated turbo may have compromised the turbine side seals.
It is often more economical to rebuild or replace a turbocharger than to pursue seal leak repairs, as seen in nine out of ten instances. If the pressure is sufficiently high to expel oil from the hot side, I would also anticipate observing leaks from the valve covers or the rear main seal.