The fleet of trucks did not come by the time of Moscow nor by Stalingrad, when lend-lease provided an insignificant part of total USSR equipment.>Anyway, you're stuck on Moscow and Stalingrad as if losing those battles would've doomed Germany in a timeline where the Soviets didn't have lend-lease
Moscow was Germany's best hope to quickly finish the war, losing that battle made sure their advance was decisively stalled and the war would protract for much longer
The loss at Stalingrad meant that>a) Germany lost all hope of seizing the Azeri oil fields/(most importantly) depriving the USSR of them>b)Germany was pushed behind so much in a single offensive that they did not just lose Stalingrad and the Caucasus, but Soviets pushed deep into Donbass as well, and shortly later began advancing on all other fronts
So yes, with or without lend lease Germany would have still been on a losing streak after Stalingrad. Not only was Germany losing massive swathes of land and had lost all hope of cutting off oil fields, but Soviets enjoyed now a complete edge in manpower/fuel/industrial production. Without lend-lease it would have been a slower and bloodier grind still resulting in Soviet victory.>15% is a small fraction
Yes, 15% of lend lease which itself was a minor contribution to the Eastern front when compared to the sheer output of Soviet industry is a small factor. At Stalingrad that 15% of lend lease would have probably translated to 5% of total Soviet equipment or less, using rough maths.>The USSR's industry is now facing a deficit of a couple hundred thousand trucks
Neither of this would have been a factor at Stalingrad, it just means the grind after Little Saturn would have been slower, but with Soviets still enjoying a total edge in production/manpower/fuel etc.