The difference between lengths (15 and 23 minutes) might just be from the frame rate difference, silent films are often shown at faster speed than originally intended because they were filmed at less than 20fps.

Uploaded for you fine folks here:

https://ok.ru/video/8620287330866
https://vk.com/video864736629_456240553
(please PM me if the links stop working)

So, if a train going into a tunnel symbolizes something in cinema, what is this movie really saying?

Sometimes, a cigar is only a cigar, methinks.