1.4.3 was the best version for NYCTA routes, and it was well optimized, but didn't have the features from newer versions like the mini map and the passenger view options. It's from 1.5 versions that it started to downgrade badly, the 1.5.1.0 and 1.5.1.2 were the worst. A while ago, I upgraded to 1.5.1.5 which seems fine, but there are still 2 issues: gray box exterior trains on some IRT SMEEs and the game locked at 40fps, even with crappy route and trains, even though I have high specs. I'm thinking of upgrading to 1.5.2 versions but I'm not sure.
Btw, it can fix most of the issues: try to run the game with high performance Nvidia or AMD graphic card by right clicking on it, your game might be running on the built in graphic card which is not powerful, so if you do so it might run a bit better and as I said fix some issues but not all of them