It's much smaller than that. You would be unlikely to find yourself in a novel position after 40 moves even if you were trying.
Edit: maybe you don't understand what i mean by novel position. I mean any position that has never been reached in the billions of lichess games, including bullet games among beginners.
Also yes I will concede that it's possible to make "quiet" moves. pawn nudges that barely affect anything. If you're doing those you're not 1500 ELO. You're intentionally trying to throw wrenches and I just don't see why an ELO bot even needs to bother with nonsense like that. This is supposed to be for fun / training!
I am around 1500 (actually 1649 on lichess blitz, but close enough).
I explored the last 5 games I played on lichess. Here are the number of moves before lichess had never seen that position before for each of the 5 games: 6, 12, 16, 15, 11.
> If you find yourself in a novel position within 10-15 moves it's likely a resignable one
The opponent is also going to be in a novel position. Should both players resign?
Just in case you think this is limited to low rated players like 1500s, look at MagnusCarlsen's most used account on Blitz: https://lichess.org/@/DrNykterstein/search?perf=2
You will see that most games become unique to the whole of lichess within 15-20 moves and a good chunk between 10-15.